A025697 - OEIS

A025697

Index of 3^n within the sequence of the numbers of the form 3^i*6^j.

1, 2, 4, 6, 9, 13, 17, 22, 27, 33, 40, 47, 55, 63, 72, 82, 92, 103, 115, 127, 140, 153, 167, 182, 197, 213, 229, 246, 264, 282, 301, 321, 341, 362, 383, 405, 428, 451, 475, 499, 524, 550, 576, 603, 630, 658, 687, 716, 746, 777, 808, 840, 872, 905, 939, 973, 1008, 1043

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

COMMENTS

Positions of zeros in A025657. - R. J. Mathar, Jul 06 2025

LINKS

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

FORMULA

From Amiram Eldar, Nov 13 2025: (Start)

A025614(a(n)) = 3^n.

a(n) = 1 + Sum_{k=0..n} ceiling(k * c), where c = log_6(3) (A152935).

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