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 A177820 #6 Jun 06 2021 09:03:36 %S A177820 1,3,7,21,381,903,921,2667,5789,6447,17367,18543,73703,114681,116967, %T A177820 208443,221109,277221,746781,797349,818769,855141,871347,1459101, %U A177820 2205609,2354961,5090367,5331669,5692701,6099429,7611387,8710041 %N A177820 Numbers k such that k^3 divides 20^(k^2) + 1. %Y A177820 Cf. A127263 (k^3 divides 2^(k^2) + 1). %Y A177820 Cf. A128678, A128679, A128680, A128681, A128682, A128683, A128684, A128685. %Y A177820 Cf. A177813, A177814, A177816, A177817, A177818, A177819, A177820. %Y A177820 Cf. A128677 (least k > p such that (k*p)^3 divides (p-1)^(k*p)^2+1, where p = prime(n) > 2). %K A177820 nonn %O A177820 1,2 %A A177820 _Alexander Adamchuk_, May 14 2010