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 A290047 #13 Jul 24 2017 11:58:54
%S A290047 2,45181,6290021506693847759,25266964023001914822246560759,
%T A290047 10384129888710330539039375199241
%N A290047 Primes in A290046.
%C A290047 For n < 26, A290046(n) are primes when n = {1, 4, 11, 15, 16}.
%C A290047 For n >= 26, 41|A290046(n). Therefore there are only 5 terms in this sequence.
%e A290047 45181 = |0!! - 3!! + 6!! - 9!! + 12!!| is prime.
%t A290047 Select[#, PrimeQ] &@ Table[Abs@ Sum[(-1)^k*(3 k)!!, {k, 0, n}], {n, 0, 30}] (* _Michael De Vlieger_, Jul 19 2017 *)
%Y A290047 Cf. A006882, A071828, A290046.
%K A290047 easy,nonn,fini,full
%O A290047 1,1
%A A290047 _XU Pingya_, Jul 19 2017