A025736 Index of 9^n within the sequence of the numbers of the form 6^i*9^j.

1, 3, 6, 10, 15, 22, 30, 39, 49, 61, 74, 88, 103, 119, 137, 156, 176, 197, 220, 244, 269, 295, 322, 351, 381, 412, 444, 478, 513, 549, 586, 625, 665, 706, 748, 791, 836, 882, 929, 977, 1027, 1078, 1130, 1183, 1237, 1293, 1350, 1408, 1467, 1528, 1590, 1653, 1717

Offset

0,2

Comments

Positions of zeros in A025662. - R. J. Mathar, Jul 06 2025

Links

Amiram Eldar, Table of n, a(n) for n = 0..10000

Formula

From Amiram Eldar, Nov 14 2025: (Start)

A025628(a(n)) = 9^n.

a(n) = 1 + Sum_{k=0..n} ceiling(k * c), where c = log_6(9) (A154009).

a(n) ~ c * n^2 / 2, where c is defined above. (End)

Mathematica

Accumulate[Table[Ceiling[n * Log[6, 9]], {n, 0, 60}]] + 1 (* Amiram Eldar, Nov 14 2025 *)

Crossrefs

Cf. A001019, A025628, A025662, A154009.

Sequence in context: A025723 A173106 A022784 * A288425 A022952 A024918

Adjacent sequences: A025733 A025734 A025735 * A025737 A025738 A025739

Keyword

nonn,easy

Author

David W. Wilson

Extensions

Offset corrected by Amiram Eldar, Nov 14 2025

Status

approved