A025638 Exponent of 2 (value of i) in n-th number of form 2^i*9^j.

0, 1, 2, 3, 0, 4, 1, 5, 2, 6, 3, 0, 7, 4, 1, 8, 5, 2, 9, 6, 3, 0, 10, 7, 4, 1, 11, 8, 5, 2, 12, 9, 6, 3, 0, 13, 10, 7, 4, 1, 14, 11, 8, 5, 2, 15, 12, 9, 6, 3, 0, 16, 13, 10, 7, 4, 1, 17, 14, 11, 8, 5, 2, 18, 15, 12, 9, 6, 3, 19, 0, 16, 13, 10, 7, 4, 20, 1, 17, 14, 11, 8, 5, 21, 2, 18, 15, 12, 9, 6, 22

Offset

1,3

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = A007814(A025611(n)). - Amiram Eldar, Nov 08 2025

Maple

N:= 10^8: # for 2^i*9^j <= N
B:= sort([seq(seq(2^i*9^j, i=0..ilog2(N/9^j)), j=0..floor(log[9](N)))]):
map(padic:-ordp, B, 2); # Robert Israel, Jun 08 2018

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[2^i*9^j, {i, 0, Log2[lim]}, {j, 0, Log[9, lim/2^i]}]] // Sort, 2]; seq[10^7] (* Amiram Eldar, Nov 08 2025 *)

Crossrefs

Cf. A007814, A025611, A025678.

Sequence in context: A021438 A195822 A356624 * A215591 A025639 A195827

Adjacent sequences: A025635 A025636 A025637 * A025639 A025640 A025641

Keyword

nonn,easy

Author

David W. Wilson

Status

approved