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%I #17 Jun 22 2018 05:14:39
%S 1,3,4,12,18,30,48,144,240,400,1152,1920,3360,6048,10080,30240,54432,
%T 90720,181440,302400,806400,1451520,2903040,4838400,8985600,16174080,
%U 31449600,56609280,139968000,264384000,497664000,1492992000,2786918400
%N Sum of unitary divisors of central binomial coefficient C(n, floor(n/2)).
%H Giovanni Resta, <a href="/A064140/b064140.txt">Table of n, a(n) for n = 1..3000</a> (first 200 terms from Harry J. Smith)
%F a(n) = A034448(A001405(n)).
%t us[n_] := If[n == 1, 1, Times @@ (1 + Power @@@ FactorInteger[n])]; Table[ us@ Binomial[n, Floor[n/2]], {n, 33}] (* _Giovanni Resta_, Jun 22 2018 *)
%o (PARI) usigma(n)= { my(f,s=1); f=factor(n); for(i=1, matsize(f)[1], s*=1 + f[i, 1]^f[i, 2]); return(s) }
%o a(n) = usigma(binomial(n, n\2)); \\ _Harry J. Smith_, Sep 08 2009
%Y Cf. A034448, A001405.
%K nonn
%O 1,2
%A _Labos Elemer_, Sep 11 2001
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