OFFSET
1,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1200
R. R. Aidagulov, M. A. Alekseyev. On p-adic approximation of sums of binomial coefficients. Journal of Mathematical Sciences 233:5 (2018), 626-634. doi:10.1007/s10958-018-3948-0 arXiv:1602.02632
MATHEMATICA
a[n_] := (2/n^3)* DivisorSum[n, MoebiusMu[n/#] Binomial[3 #, #] &]; Array[a, 50] (* G. C. Greubel, Dec 15 2017 *)
PROG
(PARI) { a(n) = sumdiv(n, d, moebius(n/d)*binomial(3*d, d))*2/n^3; }
CROSSREFS
KEYWORD
nonn
AUTHOR
Max Alekseyev, Feb 09 2016
STATUS
approved