login
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
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
LINKS
FORMULA
a(n) = 1 + A066344(n).
a(n) = 1 + floor(n*(1 + log_5(2))).
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
Sequence in context: A184117 A184624 A093001 * A224996 A373112 A246046
KEYWORD
nonn,easy,changed
AUTHOR
Clark Kimberling, Jun 16 2013
STATUS
approved