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Counted without intention to fulfill the Mitzvah:
If one unintentionally stated the Sefira of that night [i.e. without intent to fulfill the Mitzvah], he is to recount later on at night without a blessing. [This applies irrelevant of which language he answered in. This applies whether he said the days or the weeks. However, if it is the end of a week, such as day 7, 14 etc and, he only said the weeks, he is to repeat the count with a blessing.] This however only applies if one said the words “Today is such and such”. If, however, he did not say these words and rather simply said “Such and Such to the Omer”, then he is to repeat the counting with a blessing. See Halacha 18 for all the details of this ruling!
When does this apply? The above law applies starting from Bein Hashmashos [after sunset]. If the Sefira was unintentionally mentioned prior to sunset [Bein Hashmashos], but past Plag Hamincha, then he has not forfeited the blessing and is thus to repeat the count with a blessing later at night. (Nevertheless, initially, one is to be careful to avoid saying the coming nights count beginning from Plag Hamincha and onwards.)
What is the law if in during one’s Torah learning he read a text of “Today is such and such of the Omer” which matches that night’s count?
Some Poskim rule he does not fulfill his obligation, and he is hence to recount with a blessing. Other Poskim rule it is debatable if he fulfilled his obligation, and he is hence to recount without a blessing. Practically, in such a case, one is to initially avoid verbalizing the words and is rather to think it in his mind. If he already said it, then he is to recount and try to hear the blessing from another person. If he did not recount, he may continue to count the future nights with a blessing.
What is the law if prior to counting one said that “Today is Lag Baomer”, may he count that night with a blessing?
If he said the words “Today is Lag Baomer”, he does not fulfill his obligation and may count that night with a blessing. However, some conclude one is to count without a blessing. Practically, one may count with a blessing.
What is the law if prior to counting one unintentionally said “Today is Lamed Gimel Baomer” or another letter form of counting?
Should one avoid saying the words “Lag Baomer” prior to counting on the night of the 33rd?
 See Halacha 18 for all the details of this ruling
 Admur 489:12; M”A 489:8
The reason: As he fulfills his obligation according to those opinions [Rashba Brachos 13b; Ran R”H 3 in name of Geonim] who say that Mitzvos do not need intention for one to fulfill his obligation. Furthermore, even according to those Poskim [Bahag Brachos 2:7; Rif R”H 3; Rambam Shofar 2:4; Rosh R”H 3] who argue that Biblical Mitzvos require intention, today the Mitzvah of Sefira is Rabbinical, and there are Poskim [Bach 475; M”A 60:3; Admur 60:5] who rule that by a Rabbinical Mitzvah according to all one does not need intention. [Admur ibid] Accordingly, one is to be stringent like both opinions and hence is to repeat the Sefira [to suspect for the stringent opinion who rules that one is not Yotzei without intent] but without the blessing [in order to suspect for those opinions that rule one is Yotzei without intent].
 P”M 489 A”A 9; Derech Hachaim 9; Kaf Hachaim 489:54; See Admur 489:10 brought in Halacha 9!
 See Admur 489:6 [brought in Halacha 7] that we rule either the day’s or the weeks suffice during the middle days.
Other opinions: Some Poskim rule that if one did not say both the weeks and the days it is a Sfek Sfeika if he fulfills his obligation, as maybe Mitzvos need Kavana and maybe one must mention the days and weeks, and thus perhaps he is to repeat the count with a blessing. [P”M 489 M”Z 7]
 See Admur 489:6 [brought in Halacha 7] that we rule that at the end of the weeks one must count the days to be Yotzei. Vetzaruch Iyun regarding if one said the days but not the week at the end of a week, of which there is a true dispute as to whether he fulfills his obligation, and hence perhaps due to Sfek Sfeika, he would be permitted to count with a blessing, as brought in P”M 489 M”Z 7, brought in previous footnote, and as written in Admur 489:15 regarding one who answered during Plag Hamincha.
 Admur 489:15; Michaber 489:4
 Admur 489:15; Michaber ibid; Biur Halacha 489:4 “Eino”
The reason: The reason why one may recount with a blessing if the response was given after Plag Hamincha but before sunset is because we mainly rule like those who state that even after Plag Hamincha and onwards is only considered night with regards to prayer and not other matters. Furthermore, even in accordance to the opinions who rule it is consider night for all matters, there are other opinions who state that even Rabbinical Mitzvos require intention to fulfill one’s obligation. [Admur ibid]
 Admur 489:15 in parentheses; Kaf Hachaim 489:52; See Biur Halacha 489:4 “Eino”
The reason: This is in order to suspect for those opinions [See Admur ibid and 489:12] who rule that Plag Hamincha is considered night and one may hence start counting from then. [Divrei Nechemiah]
 Halachos Ketanos 1:114; Pnei Meivin 133; Yechaveh Daas 6:29; Beir Moshe 3:81; See Chasam Sofer 15 and 21; Kaf Hachaim 489:29; Piskeiy Teshuvos 489:14
 The reason: As one who is reading for the sake of learning Torah negates all other ability to be Yotzei the Mitzvah, even according to those who rule that Mitzvos do not require intent. [ibid]
 Erech Hashulchan 489:2; Beis Oveid 13, brought in Kaf Hachaim ibid
 Piskeiy Teshuvos ibid
 Kaf hachaim ibid; See Halacha 22!
 So rules even if he intended to count when he said these words: Implication of Admur 489:7; Sheilas Yaavetz 139; Siddur Yaavetz Halacha 11; Birkeiy Yosef 489:9 “I lean towards this opinion,”, brought in Shaareiy Teshuvah ibid; So rule only in this case that he did not intend to count when saying these words: Sakina Charifta 20; Maharash Levi 5; Kneses Hagedola 489; Shulchan Gavoa 489:15; Zechor Leavraham 70; Kaf Hachaim 489:30; Daas Torah 489:4
The reason: See Halacha 8 in Q&A for the full discussion on this matter, and our conclusion that Admur rules like the Yaavetz and Chida that word abbreviations are invalid number counting. Furthermore, even according to those Poskim who rule that word abbreviations is subject to a dispute in Poskim, in this case there is room to be lenient and count with a blessing even in their opinion, as there are three more doubts entered into the equation, which are a) He did not count the weeks, and b) Perhaps he we rule you need intent to fulfill the Mitzvah and c) Perhaps in order for an abbreviation to carry weight as a number one must have intent to use it as a number, and if used as a name for the Holiday, one does not fulfill his obligation according to all. [So explains Maharash Halevi, Kneses Hagedola, Sakina Charifta, Shulchan Gavoa, Zechor Leavraham and Kaf Hachaim ibid]
 Piskeiy Teshuvos 48914; Shaareiy Ezra 1:29 [Rav Ezra Batzri]
 Sakina Charifta 20; Maharash Levi 5; Kneses Hagedola 489; Shulchan Gavoa 489:15; Zechor Leavraham 70; Kaf Hachaim 489:30; Daas Torah 489:4
 The reason: As this is a case of Sfek Sfeika, as there are three doubts:disputes entered into the equation, which are a) He counted in Roshei Teivos [he did not count the actual numbers but counted letters which is a dispute if he is Yotzei]; b) He did not count the weeks, and c) Perhaps he we rule you need intent to fulfill the Mitzvah. [See Maharash Halevi, Kneses Hagedola, Sakina Charifta, Shulchan Gavoa, Zechor Leavraham and Kaf Hachaim ibid] Vetzaruch Iyun from Siddur Admur who is stringent even regarding a Sfek Sfeka.
 Piskeiy Teshuvos 48914; Shaareiy Ezra 1:29 [Rav Ezra Batzri]
 See previous footnotes and Halacha 8 in Q&A that Admur rules like the Yaavetz and Chida that word abbreviations are invalid number counting.
 Piskeiy Teshuvos 48914; Shaareiy Ezra 1:29 [Rav Ezra Batzri]; Seemingly, so would apply according to all Poskim who only allow repeating with a blessing if one said “Today is Lag Baomer” due to Sfek Sfeika, as one is not to initially enter himself into a Safek.