OFFSET
1,1
COMMENTS
All terms are primes of the form 4k+3 (A002145). A002145 is the union of {a(n)} and A129518 (numbers k > 2 such that k divides (k-2)!!-1 and (k-3)!!-1).
Primes such that ((p-1)/2)! = (-1)^((p^2-1)/8) in the finite field F_p of p elements. For example, 11 is a term since ((11-1)/2)! = 5! = -1 = (-1)^((121-1)/8) in F_11. - Luis H. Gallardo, Dec 30 2021
LINKS
Jon E. Schoenfield, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Prime@Range[2, 200], Mod[(#-1)!!-1, #]==0&] (* Giorgos Kalogeropoulos, Jan 09 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Apr 18 2007
STATUS
approved