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A064140
Sum of unitary divisors of central binomial coefficient C(n, floor(n/2)).
1
1, 3, 4, 12, 18, 30, 48, 144, 240, 400, 1152, 1920, 3360, 6048, 10080, 30240, 54432, 90720, 181440, 302400, 806400, 1451520, 2903040, 4838400, 8985600, 16174080, 31449600, 56609280, 139968000, 264384000, 497664000, 1492992000, 2786918400
OFFSET
1,2
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..3000 (first 200 terms from Harry J. Smith)
FORMULA
a(n) = A034448(A001405(n)).
MATHEMATICA
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 *)
PROG
(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) }
a(n) = usigma(binomial(n, n\2)); \\ Harry J. Smith, Sep 08 2009
CROSSREFS
Sequence in context: A026847 A026880 A026891 * A064139 A306176 A026744
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 11 2001
STATUS
approved