This Halacha is an excerpt from our Sefer
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Is an Onen obligated to recite Sefiras Haomer?
An Onen is exempt from Sefiras Haomer until after the burial. Nevertheless, if not counting will cause him to lose the ability to say a blessing on the coming nights [i.e. he is an Onen for a couple of days], he is to count without a blessing during his Aninus, and may then continue to count with a blessing on the later nights after the burial.
If the burial will take place during the day: In the event that one became an Onen at night, prior to counting Sefira, and the burial will only be taking place the next day, some Poskim rule he is not to count at night, but is rather to count the next day, after the burial, without a blessing. [Seemingly however, in such a situation, it is best to count at night without a blessing, and then count again the next day, after the burial, without a blessing.]
 Noda Beyehuda O.C. 1/27, brought in Pischeiy Teshuvah 341/6; Gilyon Maharsha 341; Rav Akiva Eiger 489; Biur Halacha 489/8 “Belo Bracha”; Kaf Hachaim 489/86; Chelkas Yaakov 3/65; Piskeiy Teshuvos 489/23; See Divrei Moshe 1/29 that the Saraf of Magalintza asked someone to count on his behalf while he stood and listened without intent to perform the Mitzvah.
Other opinions: Some Poskim rule that one cannot count Sefira during Aninus even if it causes him to lose the blessing for the remainder of Sefira. [Nehar Shalom, brought in Biur Halacha ibid]
 See Admur 71/1; Nehar Shalom, brought in Biur Halacha ibid; See however Noda Beyehuda ibid who argues that perhaps an Onen is obligated in Sefira, as it does not take very long to say and does not distract him from the Mitzvah of burial. He uses this argument to allow saying it without a blessing in the event that he may lose the blessing all together for the coming nights.
 Biur Halacha ibid in name of Nehar Shalom
 See Biur Halacha ibid that perhaps the day counting according to the opinion who allows counting by day, is a mere Tashlumin. Accordingly, it won’t help for him to count by day, the next day, even according to their opinion, as if he was exempt at night then he will also be exempt the next day even after the burial. [See Admur 71/1 and Michaber 341/2] Therefore, he should count at night in order not to forfeit the blessing, and then count again the next day after the burial.