A025681 Exponent of 9 (value of j) in n-th number of form 7^i*9^j.

0, 0, 1, 0, 1, 2, 0, 1, 2, 3, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 0, 8, 1, 2, 3, 4, 5, 6, 7, 0, 8, 1, 9, 2, 3, 4, 5, 6, 7, 0, 8, 1, 9, 2, 10, 3, 4, 5, 6, 7, 0, 8, 1, 9, 2, 10, 3, 11, 4, 5, 6, 7, 0, 8, 1, 9, 2, 10, 3, 11, 4, 12, 5, 6, 7, 0, 8, 1, 9, 2

Offset

1,6

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = A007949(A025631(n))/2. - Amiram Eldar, Nov 09 2025

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[7^i*9^j, {i, 0, Log[7, lim]}, {j, 0, Log[9, lim/7^i]}]] // Sort, 9]; seq[10^13] (* Amiram Eldar, Nov 09 2025 *)

Crossrefs

Cf. A007949, A025631, A025670.

Sequence in context: A025689 A025650 A025674 * A025659 A163351 A166352

Adjacent sequences: A025678 A025679 A025680 * A025682 A025683 A025684

Keyword

nonn,easy

Author

David W. Wilson

Status

approved