A161825 - OEIS

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

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OFFSET

1,3

LINKS

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

EXAMPLE

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.

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 *)

PROG

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

CROSSREFS

Cf. A030101.

Sequence in context: A357111 A081431 A053641 * A099551 A211206 A330717

Adjacent sequences: A161822 A161823 A161824 * A161826 A161827 A161828

KEYWORD

base,nonn

AUTHOR

Leroy Quet, Jun 20 2009

EXTENSIONS

Example corrected by Leroy Quet, Jun 21 2009

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

STATUS

approved