A025700 Index of 3^n within sequence of numbers of form 3^i * 10^j.

1, 2, 3, 5, 7, 10, 13, 17, 21, 26, 31, 37, 43, 50, 57, 65, 73, 82, 91, 101, 111, 122, 133, 144, 156, 168, 181, 194, 208, 222, 237, 252, 268, 284, 301, 318, 336, 354, 373, 392, 412, 432, 453, 474, 495, 517, 539, 562, 585, 609, 633, 658, 683, 709, 735, 762, 789, 817, 845, 874

Offset: 0

Author

David W. Wilson

Keywords

• nonn

Comments

First term different from A033638 is a(24) = 144 != A033638(24) = 145.

Positions of zeros in A025685. - R. J. Mathar, Jul 06 2025

Crossrefs

Cf. A000244, A011557.

Cf. A033638.

Programs

PARI

a(n) = vecsearch(setbinop((i,j)->3^i * 10^j, [0..n], [0..logint(10^n, 3)]), 3^n); \\ Michel Marcus, Jun 24 2023

Extensions

Offset 0 from Michel Marcus, Jun 24 2023