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 A354712 #10 Jun 04 2022 09:45:52 %S A354712 1,4,16,21,25,33,49,57,64,65,69,77,81,85,93,100,105,121,125,129,133, %T A354712 141,145,161,169,175,177,185,201,205,209,213,217,221,237,249,253,265, %U A354712 273,289,297,301,305,309,321,325,329,341,345,361,365,377,381,385,393,413,417,437,445,453,465 %N A354712 Nonprime numbers k such that the number of divisors of k divides k-1. %C A354712 Nonprime numbers k such that k == 1 (mod A000005(k)). %t A354712 Select[Range[500], ! PrimeQ[#] && Divisible[# - 1, DivisorSigma[0, #]] &] (* _Amiram Eldar_, Jun 03 2022 *) %Y A354712 Nonprime terms of A354711. %Y A354712 Cf. A000005, A033950, A272872, A354714, A354715, A354716. %K A354712 nonn %O A354712 1,2 %A A354712 _Max Alekseyev_, Jun 03 2022