A025670 Exponent of 7 (value of i) in n-th number of form 7^i*9^j.

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

Offset

1,4

Links

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

Formula

a(n) = A214411(A025631(n)). - Amiram Eldar, Nov 08 2025

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[7^i*9^j, {i, 0, Log[7, lim]}, {j, 0, Log[9, lim/7^i]}]] // Sort, 7]; seq[10^13] (* Amiram Eldar, Nov 08 2025 *)

Crossrefs

Cf. A025631, A025681, A214411.

Sequence in context: A025677 A025651 A330238 * A122200 A025646 A025661

Adjacent sequences: A025667 A025668 A025669 * A025671 A025672 A025673

Keyword

nonn,easy

Author

David W. Wilson

Status

approved