A102391 Evil numbers in evil places.

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, 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, 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

Offset: 0

Author

Paul Barry, Jan 06 2005

Keywords

• easy
• nonn
• base

Comments

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

Crossrefs

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

Programs

Mathematica

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

Python

def A102391(n): return 0 if n.bit_count()&1 else n # Chai Wah Wu, Nov 23 2023

Formula

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

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