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A057815 a(n) = GCD(n, C(n, floor(n/2))). 1

%I

%S 1,2,3,2,5,2,7,2,9,2,11,12,13,2,15,2,17,2,19,4,21,2,23,4,25,2,27,4,29,

%T 30,31,2,33,2,35,12,37,2,39,20,41,6,43,4,45,2,47,12,49,2,51,4,53,2,55,

%U 56,57,2,59,4,61,2,63,2,65,6,67,4,69,14,71,4,73,2,75,4,77,2,79,20,81,2

%N a(n) = GCD(n, C(n, floor(n/2))).

%e a(2k+1)=2k+1. For even n, a(n) is an even divisor of n: a(2k)=2,2,2,2,12,2,2,2,4,... as in A058005.

%p swing := n -> n!/iquo(n,2)!^2: seq(igcd(n,swing(n)), n=1..82); # _Peter Luschny_, May 17 2013

%Y Cf. A001405, A049077.

%K nonn

%O 1,2

%A _Labos Elemer_, Nov 13 2000

%E Offset changed to 1. _Peter Luschny_, May 17 2013

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Last modified November 20 12:37 EST 2018. Contains 317402 sequences. (Running on oeis4.)