A072976 a(n) = 2^n*binomial(3*n,n)*(3*n+2).

2, 30, 480, 7392, 110880, 1633632, 23761920, 342328320, 4895294976, 69589977600, 984515051520, 13872712089600, 194821130649600, 2728095278727168, 38106727702855680, 531128942672216064, 7388688920238489600, 102611899068766617600, 1422885000420230430720, 19703820027156391526400

Offset

0,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..100

Formula

Sum_{k>=0} 1/a(k) = (7*Pi - 24*log(2))/10 = 0.53556162416898...

a(n) ~ 3^(3*n+3/2) * sqrt(n/Pi) / 2^(n+1). - Amiram Eldar, Sep 17 2025

Mathematica

Table[2^n Binomial[3n, n](3n+2), {n, 0, 20}] (* Harvey P. Dale, Aug 20 2011 *)

Prog

(PARI) a(n)=2^n*binomial(3*n, n)*(3*n+2)
(Magma) [2^n*Binomial(3*n, n)*(3*n+2): n in [0..20]]; // Vincenzo Librandi, Aug 20 2011

Crossrefs

Cf. A005809.

Sequence in context: A219706 A318477 A219869 * A143414 A099046 A020547

Adjacent sequences: A072973 A072974 A072975 * A072977 A072978 A072979

Keyword

easy,nonn

Author

Benoit Cloitre, Aug 13 2002

Extensions

a(1) corrected by Harvey P. Dale, Aug 20 2011

Status

approved