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 A303809 #14 May 03 2018 17:46:55 %S A303809 1,2,2,4,2,4,2,4,4,4,2,8,2,4,4,16,2,8,2,8,4,4,2,8,4,4,4,8,2,8,2,4,4,4, %T A303809 4,16,2,4,4,8,2,8,2,8,8,4,2,32,4,8,4,8,2,8,4,8,4,4,2,16,2,4,8,16,4,8, %U A303809 2,8,4,8,2,16,2,4,8,8,4,8,2,32,16,4,2,16 %N A303809 Multiplicative with a(p^k) = 2^a(k). %C A303809 This sequence contains every power of 2; see A303819 for the corresponding least indices. %C A303809 For any n > 0, a(n) only depends on the prime signature of n. %H A303809 Rémy Sigrist, <a href="/A303809/b303809.txt">Table of n, a(n) for n = 1..10000</a> %F A303809 a(n) <= n with equality iff n = A014221(k) for some k >= 0. %F A303809 a(A002110(k)) = 2^k for any k >= 0. %F A303809 a(n) = 2 iff n is prime. %o A303809 (PARI) a(n) = my (f=factor(n)); prod (i=1, #f~, 2^a(f[i, 2])) %Y A303809 Cf. A002110, A014221, A061142, A303819. %K A303809 nonn,easy,mult %O A303809 1,2 %A A303809 _Rémy Sigrist_, Apr 30 2018