A025643 Exponent of 3 (value of i) in n-th number of form 3^i*8^j.

0, 1, 0, 2, 1, 3, 0, 2, 4, 1, 3, 5, 0, 2, 4, 6, 1, 3, 5, 7, 0, 2, 4, 6, 8, 1, 3, 5, 7, 9, 0, 2, 4, 6, 8, 10, 1, 3, 5, 7, 9, 11, 0, 2, 4, 6, 8, 10, 12, 1, 3, 5, 7, 9, 11, 13, 0, 2, 4, 6, 8, 10, 12, 14, 1, 3, 5, 7, 9, 11, 13, 15, 0, 2, 4, 6, 8, 10, 12, 14, 16, 1, 3, 5, 7, 9, 11, 13, 15, 17, 0, 2, 4, 6, 8, 10

Offset

1,4

Links

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

Formula

a(n) = A007949(A025615(n)). - Amiram Eldar, Nov 08 2025

Maple

N:= 10^40: # include entries for all 3^i*8^j <= N
map(t -> t[1], sort([seq(seq([i, j], j=0..floor(log[8](N/3^i))), i=0..floor(log[3](N)))], (s, t) -> 3^s[1]*8^s[2]<=3^t[1]*8^t[2]));

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[3^i*8^j, {i, 0, Log[3, lim]}, {j, 0, Log[8, lim/3^i]}]] // Sort, 3]; seq[10^9] (* Amiram Eldar, Nov 08 2025 *)

Crossrefs

Cf. A007949, A025615, A025672.

Sequence in context: A025649 A025642 A384688 * A127478 A127472 A194665

Adjacent sequences: A025640 A025641 A025642 * A025644 A025645 A025646

Keyword

nonn,easy

Author

David W. Wilson

Status

approved