A226721 Position of 2^n in the joint ranking of all the numbers 2^j for j>=0 and 5^k for k>=1; complement of A123384.

2, 3, 5, 6, 8, 9, 11, 12, 13, 15, 16, 18, 19, 21, 22, 23, 25, 26, 28, 29, 31, 32, 33, 35, 36, 38, 39, 41, 42, 43, 45, 46, 48, 49, 51, 52, 53, 55, 56, 58, 59, 61, 62, 63, 65, 66, 68, 69, 71, 72, 73, 75, 76, 78, 79, 81, 82, 83, 85, 86, 88, 89, 91, 92, 93, 95

Offset

1,1

Comments

a(n) = 1 + A066344(n).

Links

Clark Kimberling, Table of n, a(n) for n = 1..2000

Formula

a(n) = floor(n*(1 + log_c(b)).

Example

The joint ranking of the powers of 2 and of 5 begins like this: 1, 2, 4, 5, 8, 16, 25, 32, 64, 125, 128, 256, 512.  The numbers 2^n for n >= 1 are in positions 2, 3, 5, 6, 8, 9, 11, 12, 13.

Mathematica

b = 2; c=5; Floor[1 + Range[0, 100]*(1 + Log[b, c])]  (* A123384 *)
Floor[1 + Range[1, 100]*(1 + Log[c, b])]  (* A226721 *)

Crossrefs

Cf. A123384, A226720.

Sequence in context: A184117 A184624 A093001 * A224996 A246046 A026428

Adjacent sequences: A226718 A226719 A226720 * A226722 A226723 A226724

Keyword

nonn,easy

Author

Clark Kimberling, Jun 16 2013

Status

approved