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 A180963 #15 Aug 06 2023 03:06:23 %S A180963 21,42,69,81,84,87,93,117,138,162,168,171,174,186,213,234,261,273,276, %T A180963 279,285,309,321,324,327,333,336,339,342,345,348,351,357,369,372,375, %U A180963 381,405,426,453,465,468,471,477,501,522,546,552,555,558,570,597,618 %N A180963 Numbers divisible by 3 with an odd number of 1s in their base 2 representation. %C A180963 Not the same as multiples of 3 with a nonzero alternating binary digit sum: a(142) = 1368, but that sequence has 1365 as the 142nd term. - _Charles R Greathouse IV_, Feb 06 2015 %H A180963 Charles R Greathouse IV, <a href="/A180963/b180963.txt">Table of n, a(n) for n = 1..10000</a> %F A180963 a(n) = 3*A036556(n). - _Amiram Eldar_, Aug 06 2023 %t A180963 Select[3 * Range[210], OddQ[DigitCount[#, 2, 1]] &] (* _Amiram Eldar_, Aug 06 2023 *) %o A180963 (PARI) isok(n) = (hammingweight(n) % 2) && (n % 3 == 0) \\ _Michel Marcus_, Jul 16 2013 %Y A180963 Intersection of A000069 and A008585. %Y A180963 Cf. A036556. %K A180963 nonn,easy,base %O A180963 1,1 %A A180963 _Dylan Hamilton_, Sep 28 2010