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 A129516 #7 Jun 08 2021 02:27:23 %S A129516 1,2,8,11,16,19,23,31,32,43,64,67,71,128,131,151,163,167,179,223,227, %T A129516 239,256,271,311,347,359,419,439,443,463,487,491,512,523,563,571,619, %U A129516 647,683,691,719,739,751,787,911,919,947,967,983,1019,1024,1031,1039 %N A129516 Numbers k such that k divides (k-1)!! - 1. %C A129516 Terms include all powers of 2 except 2^2 and some primes of the form 4m+3 belonging to A002145. Odd primes in this sequence are listed in A129517. A002145 is the union of A129517 and A129518 (numbers m > 2 such that m divides (m-2)!!-1 and (m-3)!!-1). %t A129516 Select[Range[2048],IntegerQ[((#-1)!!-1)/# ]&] %Y A129516 Cf. A006882 (double factorials). %Y A129516 Cf. A002145 (primes of the form 4k+3). %Y A129516 Cf. A129517 (odd primes p such that p divides (p-1)!!-1). %Y A129516 Cf. A129518 (numbers k > 2 such that k divides (k-2)!!-1 and (k-3)!!-1). %K A129516 nonn %O A129516 1,2 %A A129516 _Alexander Adamchuk_, Apr 18 2007