OFFSET
1,2
LINKS
V. J. W. Guo and J. Zeng, A note on two identities arising from enumeration of convex polyominoes, J. Comp. Appl. Math. 180 (2005) pp 413-423.
EXAMPLE
Triangle is symmetric in the two indices and starts
1,
3, 18,
6, 60, 300,
10, 150, 1050, 4900,
15, 315, 2940, 17640, 79380,
21, 588, 7056, 52920, 291060, 1280664,
MAPLE
a := proc(n, m) m*n*(binomial(m+n, n))^2/2/(m+n) ; end: for n from 1 to 10 do for m from 1 to n do printf("%d, ", a(n, m)) ; od: od:
MATHEMATICA
Flatten[Table[m*n*Binomial[m+n, m]^2/(2(m+n)), {n, 10}, {m, n}]] (* Harvey P. Dale, Dec 24 2011 *)
PROG
(PARI) A131635(n, m) = m*n*binomial(m+n, m)^2/(2*(m+n))
CROSSREFS
KEYWORD
AUTHOR
R. J. Mathar, Sep 05 2007
STATUS
approved