A161825 a(n) is the GCD of n and {the number made by reversing the order of the digits of n written in binary}.

1, 1, 3, 1, 5, 3, 7, 1, 9, 5, 1, 3, 1, 7, 15, 1, 17, 9, 1, 5, 21, 1, 1, 3, 1, 1, 27, 7, 1, 15, 31, 1, 33, 17, 7, 9, 1, 1, 3, 5, 1, 21, 1, 1, 45, 1, 1, 3, 7, 1, 51, 1, 1, 27, 1, 7, 3, 1, 1, 15, 1, 31, 63, 1, 65, 33, 1, 17, 3, 7, 1, 9, 73, 1, 15, 1, 1, 3, 1, 5, 3, 1, 1, 21, 85, 1, 3, 1, 1, 45, 1, 1, 93, 1

Offset: 1

Author

Leroy Quet, Jun 20 2009

Keywords

• base
• nonn

Examples

			70 in binary is 1000110. Reversing this (and ignoring the leading 0), we have 110001, which is 49 in decimal. Therefore a(70) = gcd(70,49) = 7.
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A030101.

Programs

Maple

A030101 := proc(n) local bdgs; bdgs := convert(n,base,2) ; add( op(-i,bdgs)*2^(i-1), i=1..nops(bdgs)) ; end: A161825 := proc(n) gcd(A030101(n),n) ; end: seq(A161825(n),n=1..100) ; # R. J. Mathar, Jul 04 2009

Mathematica

Array[GCD[#, IntegerReverse[#, 2]] &, 94] (* Michael De Vlieger, Feb 24 2019 *)

PARI

a(n) = gcd(n, fromdigits(Vecrev(binary(n)), 2)); \\ Michel Marcus, Feb 25 2019

Extensions

Example corrected by Leroy Quet, Jun 21 2009

a(4) corrected and sequence extended by R. J. Mathar, Jul 04 2009