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%I #8 Sep 05 2017 03:12:51
%S 0,1,1,2,3,2,3,4,4,3,5,4,3,4,5,6,8,6,9,8,8,8,7,7,6,7,9,10,10,10,11,11,
%T 12,12,13,12,12,11,13,12,13,13,12,14,14,13,15,14,15,15,15,15,18,17,17,
%U 17,17,18,17,18,17,18,18,19,21,20,22,19,19,19,21,19,19,20,20,23,23,22
%N Number of unitary prime divisors of the n-th Catalan number.
%F a(n) = A056169(A000108(n)).
%e n = 10: Catalan(20) = 16796 = 2*2*13*17*19, unitary p-divisors = {13,17,19}, so a(20) = 3.
%o (PARI) nbupd(n) = my(f=factor(n)[, 2]); sum(i=1, #f, f[i]==1);
%o a(n) = nbupd(binomial(2*n, n)/(n+1)); \\ _Michel Marcus_, Sep 05 2017
%Y Cf. A000108, A034444, A048105, A056169, A056170, A080405, A081386, A081387, A081389.
%K nonn
%O 1,4
%A _Labos Elemer_, Mar 27 2003
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