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 A118731 #9 Jul 11 2025 15:35:25 %S A118731 0,4,5,7,8,10,12,16,18,19,20,22,23,24,25,27,28,29,30,31,34,35,38,39, %T A118731 40,48,49,52,53,56,59,62,63,66,68,69,72,75,81,87,88,89,92,93,94,96,97, %U A118731 99,100,101,104,105,108,109,110,111,114,118,119,121,125,127,131,132,133 %N A118731 Numbers k such that 2^k has odd digit sum. %t A118731 Select[Range[0, 133], Mod[ Plus @@ IntegerDigits[2^# ], 2] == 1 &] (* _Ray Chandler_, Jun 10 2006 *) %Y A118731 Cf. A118732, A118735, A076203. %K A118731 base,nonn %O A118731 1,2 %A A118731 _Zak Seidov_, May 22 2006