This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A290045 #14 Jul 24 2017 11:57:31
%S A290045 7,41,176075177,49127973630377
%N A290045 Primes in A290044.
%C A290045 For n < 20, A290044(n) are prime when n = {2, 3, 9, 13}.
%C A290045 For n >= 20, 19|A290044(n). Therefore there are only 4 terms in this sequence.
%e A290045 41 = |0!! - 2!! + 4!! - 6!!| is prime.
%t A290045 Select[Table[Abs@ Sum[(-1)^k*(2 k)!!, {k, 0, n}], {n, 0, 60}], PrimeQ] (* _Michael De Vlieger_, Jul 19 2017 *)
%Y A290045 Cf. A006882, A071828, A290044.
%K A290045 nonn,fini,full
%O A290045 1,1
%A A290045 _XU Pingya_, Jul 19 2017