A102391 - OEIS

%I #13 Nov 23 2023 15:16:39

%S 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 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 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 Evil numbers in evil places.

%C Evil numbers A001969(n) appear at positions indexed by the evil numbers, 0 otherwise. A001477(n) = A102391(n) + A102392(n).

%F a(n) = if((1+floor(n/2)) (1+(-1)^A000120(n))/2 = 0, 0, n).

%F a(n) = if((1+floor(n/2)) (1+(-1)^A010060(n))/2 = 0, 0, n).

%t a[n_] := If[EvenQ @ DigitCount[n, 2, 1], n, 0]; Array[a, 100, 0] (* _Amiram Eldar_, Aug 02 2020 *)

%o (Python)

%o def A102391(n): return 0 if n.bit_count()&1 else n # _Chai Wah Wu_, Nov 23 2023

%Y Cf. A000120, A001477, A001969, A010060, A102391, A102392.

%K easy,nonn,base

%O 0,4

%A _Paul Barry_, Jan 06 2005