A374072 Integers of the form x!*y!/(x! + y!) where x, y are positive integers.

1, 3, 12, 20, 60, 360, 630, 2520, 4480, 20160, 36288, 181440, 1814400, 3326400, 19958400, 239500800, 444787200, 3113510400, 5811886080, 43589145600, 81729648000, 653837184000, 1302884352000, 10461394944000, 19760412672000, 177843714048000, 3201186852864000

Offset

1,2

Comments

The sequence contains A001710 when x=y.

Links

Table of n, a(n) for n=1..27.

Example

630 is in the sequence because with x=6 and y=7, 6!7!/(6!+7!) = 720*5040/(720+5040)=630.

Prog

(PARI) lista(nn) = select(x->(denominator(x)==1), setbinop((x, y)->x!*y!/(x! + y!), [1..nn])) \\ Michel Marcus, Jun 27 2024

Crossrefs

Cf. A001710.

Sequence in context: A122576 A212760 A143268 * A193558 A256131 A080767

Adjacent sequences: A374069 A374070 A374071 * A374073 A374074 A374075

Keyword

nonn

Author

Michel Lagneau, Jun 27 2024

Status

approved