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

Author

Clark Kimberling

Keywords

• nonn
• base

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).

Examples

			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
		

Links

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

Crossrefs

Cf. A050608.

Programs

Mathematica

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