OFFSET
1,2
REFERENCES
Foulds, L. R. Enumeration of graph theoretic solutions for facilities layout. Proceedings of the sixteenth Southeastern international conference on combinatorics, graph theory and computing (Boca Raton, Fla., 1985). Congr. Numer. 48 (1985), 87--99. MR0830702(87f:90045). See Table 2. - From N. J. A. Sloane, Apr 06 2012
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
William T. Tutte, A census of planar triangulations, Canad. J. Math. 14 (1962), 21-38.
FORMULA
a(n) ~ 2^(2+8*n)*3^(-7/2-3*n)*exp(-n)*n^n. - Stefano Spezia, Aug 03 2022
MATHEMATICA
Table[Binomial[n+3, 2] (4n+1)!/(3n+3)!, {n, 20}] (* Harvey P. Dale, May 16 2012 *)
PROG
(Magma) [Binomial(n+3, 2)*Factorial(4*n+1)/Factorial(3*n+3): n in [1..20]]; // Vincenzo Librandi, May 21 2012
(Python)
from math import factorial
def A007816(n): return ((n*(n + 5) + 6)*factorial((n<<2)+1)>>1)//factorial(3*(n+1)) # Chai Wah Wu, Nov 17 2022
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
Victor Reiner (reiner(AT)math.umn.edu), Paul Edelman (edelman(AT)math.umn.edu)
STATUS
approved