A025706 - OEIS

A025706

Index of 5^n within sequence of numbers of form 4^i*5^j.

1, 3, 6, 10, 15, 21, 28, 37, 47, 58, 70, 83, 97, 113, 130, 148, 167, 187, 208, 231, 255, 280, 306, 333, 361, 391, 422, 454, 487, 521, 556, 592, 630, 669, 709, 750, 792, 835, 880, 926, 973, 1021, 1070, 1120, 1172, 1225, 1279, 1334, 1390, 1447, 1506, 1566, 1627, 1689

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

OFFSET

0,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 0..10000

PROG

(PARI) a(n)=my(N=1); n+1+sum(i=1, n, logint(N*=5, 4)); \\ Charles R Greathouse IV, Jan 11 2018

(PARI) first(n)=my(s, N=1/5); vector(n+1, i, s+=logint(N*=5, 4)+1) \\ Charles R Greathouse IV, Jan 11 2018

CROSSREFS

Differs from A025730 at a(56).

Sequence in context: A120721 A122056 A358038 * A025730 A066353 A179653

Adjacent sequences: A025703 A025704 A025705 * A025707 A025708 A025709