A025665 Exponent of 7 (value of j) in n-th number of form 3^i*7^j.

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

Offset

1,7

Links

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

Formula

a(n) = A214411(A003594(n)). - Amiram Eldar, Nov 08 2025

Mathematica

seq[lim_] := IntegerExponent[Flatten[Table[3^i*7^j, {i, 0, Log[3, lim]}, {j, 0, Log[7, lim/3^i]}]] // Sort, 7]; seq[10^9] (* Amiram Eldar, Nov 08 2025 *)

Crossrefs

Cf. A003594, A025642, A214411.

Sequence in context: A330759 A216607 A025672 * A357022 A025841 A138468

Adjacent sequences: A025662 A025663 A025664 * A025666 A025667 A025668

Keyword

nonn,easy

Author

David W. Wilson

Status

approved