OFFSET
1,2
COMMENTS
We discovered that the numbers that appear in the lower left triangle of the ED2 array A167560 (m <= n) behave in a regular way, see the formula below. This rather simple regularity doesn't show up in the upper right triangle of the ED2 array (m > n).
LINKS
G. C. Greubel, Table of n, a(n) for the first 50 rows
FORMULA
a(n,m) = 4^(m-1)*(m-1)!*(n+m-1)!/(2*m-1)!.
EXAMPLE
The first few triangle rows are:
[1]
[2, 4]
[6, 16, 32]
[24, 80, 192, 384]
[120, 480, 1344, 3072, 6144]
[720, 3360, 10752, 27648, 61440, 122880]
MAPLE
a := proc(n, m): 4^(m-1)*(m-1)!*(n+m-1)!/(2*m-1)! end: seq(seq(a(n, m), m=1..n), n=1..8); # Johannes W. Meijer, revised Nov 23 2012
MATHEMATICA
Flatten[Table[4^(m - 1)*(m - 1)!*(n + m - 1)!/(2*m - 1)!, {n, 1, 50}, {m, n}]] (* G. C. Greubel, Jun 16 2016 *)
CROSSREFS
KEYWORD
AUTHOR
Johannes W. Meijer, Nov 10 2009
STATUS
approved