A151780 a(n) = 5^(wt(n) - 1) where wt(n) = A000120(n).

1, 1, 5, 1, 5, 5, 25, 1, 5, 5, 25, 5, 25, 25, 125, 1, 5, 5, 25, 5, 25, 25, 125, 5, 25, 25, 125, 25, 125, 125, 625, 1, 5, 5, 25, 5, 25, 25, 125, 5, 25, 25, 125, 25, 125, 125, 625, 5, 25, 25, 125, 25, 125, 125, 625, 25, 125, 125, 625, 125, 625, 625, 3125, 1, 5, 5, 25, 5, 25, 25, 125, 5

Offset

1,3

Links

Paolo Xausa, Table of n, a(n) for n = 1..10000

Example

From Omar E. Pol, Jul 21 2009: (Start)
If written as a triangle:
  1;
  1,5;
  1,5,5,25;
  1,5,5,25,5,25,25,125;
  1,5,5,25,5,25,25,125,5,25,25,125,25,125,125,625;
  1,5,5,25,5,25,25,125,5,25,25,125,25,125,125,625,5,25,25,125,25,125,125,625,...
(End)

Mathematica

5^(DigitSum[Range[100], 2] - 1) (* Paolo Xausa, Feb 18 2026 *)

Prog

(Python)
def A151780(n): return 5**(n.bit_count()-1) # Chai Wah Wu, Nov 15 2022
(PARI) a(n) = 5^(hammingweight(n)-1); \\ Michel Marcus, Nov 15 2022

Crossrefs

Essentially A151779/6.

Cf. A000120, A048881, A048896, A147610, A151783.

Cf. A000351. - Omar E. Pol, Jul 21 2009

Sequence in context: A198366 A162797 A087232 * A054244 A093562 A081774

Adjacent sequences: A151777 A151778 A151779 * A151781 A151782 A151783

Keyword

nonn

Author

N. J. A. Sloane, Jun 25 2009

Status

approved