A025741 Index of 10^n within sequence of numbers of form 3^i*10^j.

1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 145, 171, 199, 229, 261, 295, 331, 369, 409, 451, 496, 543, 592, 643, 696, 751, 808, 867, 928, 991, 1056, 1124, 1194, 1266, 1340, 1416, 1494, 1574, 1656, 1740, 1826, 1915, 2006, 2099, 2194, 2291, 2390, 2491, 2594, 2699

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• easy

Comments

Positions of zeros in A025644. - R. J. Mathar, Jul 06 2025

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Programs

PARI

a(n)=my(N=1); n+sum(i=2,n, logint(N*=10,3)); \\ Charles R Greathouse IV, Jan 10 2018

PARI

first(n)=my(s,N=1/10); vector(n,i, s+=logint(N*=10,3)+1) \\ Charles R Greathouse IV, Jan 10 2018