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 A213337 #22 Jul 24 2021 05:39:23 %S A213337 143,399,527,779,1501,1679,2407,2627,2703,2737,3239,3289,3599,3827, %T A213337 4031,4033,4879,4991,5183,5291,5719,5921,6479,6601,6721,7739,8321, %U A213337 8687,8903,9361,9503,10153,10439,11537,11663 %N A213337 Odd composite numbers k that divide the imaginary part of (1+2i)^A201629(k). %C A213337 The odd terms of A212502. %H A213337 Amiram Eldar, <a href="/A213337/b213337.txt">Table of n, a(n) for n = 1..10000</a> %t A213337 t[n_]:=Which[Mod[n,4]==3,n+1,Mod[n,4]==1,n-1,True,n]; Select[1+ Range[1000], Mod[#,2]==1&&! PrimeQ[#] && Im[PowerMod[1 + 2I, t[#], #]] == 0 &] %Y A213337 Cf. A201629, A212502. %K A213337 nonn %O A213337 1,1 %A A213337 _José María Grau Ribas_, Jun 09 2012