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%I #3 Mar 30 2012 17:26:52
%S 0,1,1,2,3,4,3,6,7,8,9,10,9,12,13,12,15,16,15,18,17,20,21,22,23,24,25,
%T 26,25,28,29,30,31,32,33,34,35,36,37,38,39,40,39,42,43,42,45,46,47,48,
%U 49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,63,66,67,68,69,70,71
%N a(1) = 0; a(n) = the least k such that ((n+1)(n+2)(n+3)...(n+k))/((n-1)(n-2)(n-3)...(n-k)) is an integer (see A092935).
%o (PARI) { a(n) = local(p, q, r); p=1; q=1; for(k=1,n, p*=n+k; q*=n-k; r=gcd(p,q); p\=r; q\=r; if(q==1,return(k))) }
%Y Cf. A092935.
%K nonn
%O 1,4
%A _Max Alekseyev_, Feb 11 2005
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