A025708 Index of 5^n within sequence of numbers of form 5^i*7^j.

1, 2, 4, 7, 11, 16, 21, 27, 34, 42, 51, 61, 71, 82, 94, 107, 121, 136, 151, 167, 184, 202, 221, 241, 261, 282, 304, 327, 351, 375, 400, 426, 453, 481, 510, 539, 569, 600, 632, 665, 699, 733, 768, 804, 841, 879, 918, 957, 997, 1038, 1080, 1123, 1167, 1211, 1256, 1302

Offset: 0

Author

David W. Wilson

Keywords

• nonn

Comments

Position of zeros in A025667.- R. J. Mathar, Jul 06 2025

Links

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

Programs

PARI

a(n)=my(N=1); n+1+sum(i=1, n, logint(N*=5, 7)); \\ Charles R Greathouse IV, Jan 11 2018

PARI

first(n)=my(s, N=1/5); vector(n+1, i, s+=logint(N*=5, 7)+1) \\ Charles R Greathouse IV, Jan 11 2018

Extensions

Offset corrected by Charles R Greathouse IV, Jan 11 2018