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 A320026 #7 Oct 14 2018 03:50:56 %S A320026 1,3,7,15,21,31,127,1023,8191,131071,180213,524287,1796165,3112865, %T A320026 5388495,9338595,2147483647,2305843009213693951, %U A320026 618970019642690137449562111,162259276829213363391578010288127,170141183460469231731687303715884105727 %N A320026 Odd squarefree numbers k for which m >= 0 can be found such that k*2^m divides sigma(k*2^m). %C A320026 The Mersenne primes A000668 are a subsequence. %e A320026 1023 is in this sequence because 1023 = 3*11*31 and 1023*2^9 divides 1571328 which is the sum of divisors of 1023*2^9. %Y A320026 Cf. A000203, A000668, A007691, A056911, A320024. %K A320026 nonn %O A320026 1,2 %A A320026 _Peter Luschny_, Oct 13 2018