A022335 Index of 2^n within sequence of numbers of form 2^i * 5^j.

1, 2, 3, 5, 7, 10, 13, 17, 21, 25, 30, 35, 41, 47, 54, 61, 68, 76, 84, 93, 102, 112, 122, 132, 143, 154, 166, 178, 191, 204, 217, 231, 245, 260, 275, 291, 307, 323, 340, 357, 375, 393, 412, 431, 450, 470, 490, 511, 532, 554, 576, 598, 621, 644, 668, 692, 717, 742, 767, 793

Offset: 0

Author

Clark Kimberling

Keywords

• nonn

Comments

Greedy inverse of A022332: a(n) = min {k : A022332(k) = n}. - R. J. Mathar, Aug 04 2016

Links

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

Crossrefs

Cf. A003592, A022334.

Programs

Mathematica

Table[1 + Sum[Ceiling[j*Log[5, 2]], {j, i}], {i, 0, 59}] (* Michael De Vlieger, Feb 08 2023 *)

PARI

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

Formula

a(n) = Sum_{i=0..n} (1 + floor(log_5(2^i))). - Michel Marcus, Oct 02 2013