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 A102391 #13 Nov 23 2023 15:16:39 %S A102391 0,0,0,3,0,5,6,0,0,9,10,0,12,0,0,15,0,17,18,0,20,0,0,23,24,0,0,27,0, %T A102391 29,30,0,0,33,34,0,36,0,0,39,40,0,0,43,0,45,46,0,48,0,0,51,0,53,54,0, %U A102391 0,57,58,0,60,0,0,63,0,65,66,0,68,0,0,71,72,0,0,75,0,77,78,0,80,0,0,83,0,85 %N A102391 Evil numbers in evil places. %C A102391 Evil numbers A001969(n) appear at positions indexed by the evil numbers, 0 otherwise. A001477(n) = A102391(n) + A102392(n). %F A102391 a(n) = if((1+floor(n/2)) (1+(-1)^A000120(n))/2 = 0, 0, n). %F A102391 a(n) = if((1+floor(n/2)) (1+(-1)^A010060(n))/2 = 0, 0, n). %t A102391 a[n_] := If[EvenQ @ DigitCount[n, 2, 1], n, 0]; Array[a, 100, 0] (* _Amiram Eldar_, Aug 02 2020 *) %o A102391 (Python) %o A102391 def A102391(n): return 0 if n.bit_count()&1 else n # _Chai Wah Wu_, Nov 23 2023 %Y A102391 Cf. A000120, A001477, A001969, A010060, A102391, A102392. %K A102391 easy,nonn,base %O A102391 0,4 %A A102391 _Paul Barry_, Jan 06 2005