A068514 Numbers of the form (2i)! (2j)! / i! j! (i + j)!.

1, 2, 4, 6, 10, 12, 20, 28, 40, 70, 72, 84, 90, 140, 198, 220, 252, 264, 308, 504, 572, 728, 858, 924, 1092, 1560, 1716, 1820, 1848, 2520, 2860, 3432, 3960, 4420, 4760, 5304, 6120, 6864, 8976, 9724, 12870, 12920, 14586, 15504, 16796, 21318, 25740

Offset

1,2

Links

Table of n, a(n) for n=1..47.

Example

90 is in the sequence because for a&b = 3&5, 6! 10!/(3! 5! 8!) = 90.

Mathematica

Flatten[Table[((2i)!(2j)!)/(i! j! (i+j)!), {i, 0, 10}, {j, 0, 10}]]//Union (* Harvey P. Dale, May 31 2019 *)

Crossrefs

Sequence in context: A293821 A194944 A133871 * A074645 A125286 A045963

Adjacent sequences: A068511 A068512 A068513 * A068515 A068516 A068517

Keyword

nonn

Author

Robert G. Wilson v, Mar 19 2002

Status

approved