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 A118730 #10 May 05 2025 01:30:16 %S A118730 1,2,3,6,9,11,13,14,15,17,21,26,32,33,36,37,41,42,43,44,45,46,47,50, %T A118730 51,54,55,57,58,60,61,64,65,67,70,71,73,74,76,77,78,79,80,82,83,84,85, %U A118730 86,90,91,95,98,102,103,106,107,112,113,115,116,117,120,122,123,124,126 %N A118730 Numbers k such that 2^k has even digit sum. %H A118730 Robert Israel, <a href="/A118730/b118730.txt">Table of n, a(n) for n = 1..10000</a> %p A118730 filter:= proc(n) convert(convert(2^n,base,10),`+`)::even end proc: %p A118730 select(filter, [$1..1000]); # _Robert Israel_, Apr 12 2021 %t A118730 Select[Range[126], Mod[ Plus @@ IntegerDigits[2^# ], 2] == 0 &] (* _Ray Chandler_, Jun 10 2006 *) %Y A118730 Cf. A118733, A118734. %K A118730 nonn,base %O A118730 1,2 %A A118730 _Zak Seidov_, May 22 2006