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A263931 a(n) = binomial(2*n, n) / Product(p prime | n < p <= 2*n). 0

%I

%S 1,1,2,4,2,36,12,24,90,20,4,168,28,1400,5400,720,90,5940,23100,46200,

%T 180180,17160,1560,140400,11700,45864,179928,13328,52360,5969040,

%U 397936,795872,3133746,12345060,726180,2863224,159068,318136,1255800,4958800,247940

%N a(n) = binomial(2*n, n) / Product(p prime | n < p <= 2*n).

%C The highest exponent in the prime factorization of a(n) is A263922(n), n>=2.

%C a(n) is even for n>=2.

%F a(n) = A000984(n)/A261130(n).

%p a := n -> binomial(2*n,n)/convert(select(isprime, {$n+1..2*n}),`*`):

%p seq(a(n), n=0..40);

%Y Cf. A000984, A261130, A263922.

%K nonn

%O 0,3

%A _Peter Luschny_, Oct 31 2015

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Last modified May 25 23:10 EDT 2020. Contains 334597 sequences. (Running on oeis4.)