Integers of the form x!*y!/(x! + y!) where x, y are positive integers.

Terms

a(0) =1a(1) =3a(2) =12a(3) =20a(4) =60a(5) =360a(6) =630a(7) =2520a(8) =4480a(9) =20160a(10) =36288a(11) =181440a(12) =1814400a(13) =3326400a(14) =19958400a(15) =239500800a(16) =444787200a(17) =3113510400a(18) =5811886080a(19) =43589145600a(20) =81729648000a(21) =653837184000