A022334 Index of 5^n within sequence of numbers of form 2^i * 5^j.

1, 4, 9, 16, 26, 38, 52, 69, 88, 109, 133, 159, 187, 218, 251, 286, 324, 364, 406, 451, 498, 547, 599, 653, 709, 768, 829, 892, 958, 1026, 1096, 1168, 1243, 1320, 1399, 1481, 1565, 1651, 1740, 1831, 1924, 2020, 2118, 2218, 2321, 2426, 2533, 2643, 2755, 2869, 2986

Offset: 0

Author

Clark Kimberling

Keywords

• nonn

Comments

Greedy inverse of A022333: a(n) = min{k: A022333(k) = n}. - R. J. Mathar, Aug 04 2016

Links

• Michael De Vlieger, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A003592, A022335.

Programs

Mathematica

Table[1 + Sum[Ceiling[j*Log[2, 5]], {j, i}], {i, 0, 50}] (* Michael De Vlieger, Feb 08 2023 *)

PARI

a(n) = sum(i=0, n, 1 + floor(log(5^i)/log(2))); \\ Michel Marcus, Oct 02 2013

Formula

a(n) = Sum_{i=0..n} 1 + floor(log(5^i)/log(2)). - Michel Marcus, Oct 02 2013