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A161825
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a(n) is the GCD of n and {the number made by reversing the order of the digits of n written in binary}.
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2
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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
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1,3
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LINKS
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EXAMPLE
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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.
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MAPLE
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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
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MATHEMATICA
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PROG
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(PARI) a(n) = gcd(n, fromdigits(Vecrev(binary(n)), 2)); \\ Michel Marcus, Feb 25 2019
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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a(4) corrected and sequence extended by R. J. Mathar, Jul 04 2009
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STATUS
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approved
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