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 A371970 #15 Apr 25 2024 06:35:33 %S A371970 1,2,3,5,6,8,9,12,14,17,18,21,23,24,25,26,27,31,32,33,35,37,38,39,40, %T A371970 42,44,45,47,51,52,55,57,58,59,60,61,64,70,71,72,73,74,75,76,77,78,79, %U A371970 81,96,99,102,104,105,106,109,112,116,127,131,132,133,134,135,136 %N A371970 Exponents k such that the binary expansion of 3^k has an even number of ones. %H A371970 Hugo Pfoertner, <a href="/A371970/b371970.txt">Table of n, a(n) for n = 1..10000</a> %p A371970 q:= n-> is(add(i, i=Bits[Split](3^n))::even): %p A371970 select(q, [$0..150])[]; # _Alois P. Heinz_, Apr 24 2024 %t A371970 Select[Range[136], EvenQ@ DigitCount[3^#, 2, 1] &] (* _Michael De Vlieger_, Apr 24 2024 *) %o A371970 (PARI) is_a371970(k) = hammingweight(3^k)%2 == 0 %Y A371970 Complement of A223024. %Y A371970 Cf. A000120, A000244, A001969, A011754, A078839. %K A371970 nonn,base,easy %O A371970 1,2 %A A371970 _Hugo Pfoertner_, Apr 24 2024