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%I #3 Mar 30 2012 18:50:35
%S 1,2,3,6,5,190,7,2415,84,31626,11,
%T 10485409451852020512869123005636410508621081799664615969238750,13,
%U 5887596,4509005501,652786136966869378239977875665,17
%N a(n)=b(n,n) with b(n,1)=n and b(n,k)=binomial(b(n,k-1),d(n,n-k+1)) for 1<k<=n, where d(n,i) are the divisors of n, d(i)<d(j), 1<=i<j<=A000005(n).
%C n>1: a(n) = n iff n is prime;
%C a(18) > 10^150.
%e Set of divisors of n=10: {1,2,5,10}, binomial(10,5)=252 ->
%e binomial(252,2)=31626 -> binomial(31626,1)=31626=a(10).
%K nonn
%O 1,2
%A _Reinhard Zumkeller_, Jun 28 2003
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