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 A081730 #23 Apr 22 2025 02:45:13
%S A081730 1,2,3,4,5,7,8,11,13,15,16,17,19,23,29,31,32,37,41,43,47,53,59,61,64,
%T A081730 67,71,73,79,83,89,91,97,101,103,107,109,113,127,128,131,137,139,149,
%U A081730 151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241
%N A081730 Numbers k such that the k-th Euler number == 1 (mod k).
%C A081730 All primes and all powers of 2 are in the sequence. The composite terms that are not powers of 2 are in A035163.
%H A081730 Amiram Eldar, <a href="/A081730/b081730.txt">Table of n, a(n) for n = 1..2000</a>
%t A081730 Select[Range[250], Divisible[Abs[EulerE[2*#]] - 1, #] &] (* _Amiram Eldar_, Apr 22 2025 *)
%o A081730 (PARI) a000364(n)=subst(bernpol(2*n+1), 'x, 1/4)*4^(2*n+1)*(-1)^(n+1)/(2*n+1);
%o A081730 lista(nn) = {for (n=1, nn, if (Mod(a000364(n), n) == 1, print1(n, ", ")););} \\ _Michel Marcus_, Apr 18 2015
%Y A081730 Union of A035163 and A174090.
%Y A081730 Cf. A000079, A000364, A065091, A069042.
%K A081730 nonn
%O A081730 1,2
%A A081730 _Benoit Cloitre_, Apr 06 2003
%E A081730 More terms from Weston Markham (weston.markham(AT)gmail.com), May 22 2005