A037461 a(n)=Sum{d(i)*7^i: i=0,1,...,m}, where Sum{d(i)*4^i: i=0,1,...,m} is the base 4 representation of n.

1, 2, 3, 7, 8, 9, 10, 14, 15, 16, 17, 21, 22, 23, 24, 49, 50, 51, 52, 56, 57, 58, 59, 63, 64, 65, 66, 70, 71, 72, 73, 98, 99, 100, 101, 105, 106, 107, 108, 112, 113, 114, 115, 119, 120, 121, 122, 147, 148, 149, 150, 154, 155, 156, 157

Offset

1,2

Comments

A number k is a term of this sequence if and only if 7 divides neither C(2*k-1,k) nor C(2*k,k).

Links

Clark Kimberling, Table of n, a(n) for n = 1..1000

Example

39 = 3*1 + 1*4 + 2*4^2 -> 3*1 + 1*7 + 3*7^2 = 108, so a(39) = 108. - Clark Kimberling, Jul 30 2012

Mathematica

Table[FromDigits[RealDigits[n, 4], 7], {n, 1, 100}]
(* Clark Kimberling, Aug 02 2012 *)

Crossrefs

Cf. A050608.

Sequence in context: A154432 A251391 A047361 * A284514 A268398 A249587

Adjacent sequences: A037458 A037459 A037460 * A037462 A037463 A037464

Keyword

nonn,base

Author

Clark Kimberling

Status

approved