A139149 a(n) = (n!+2)/2.

2, 4, 13, 61, 361, 2521, 20161, 181441, 1814401, 19958401, 239500801, 3113510401, 43589145601, 653837184001, 10461394944001, 177843714048001, 3201186852864001, 60822550204416001, 1216451004088320001, 25545471085854720001, 562000363888803840001

Offset: 2

Author

Artur Jasinski, Apr 11 2008

Keywords

• nonn
• easy

Comments

Also the number of (not necessarily maximal) cliques in the (n-1)-(weak) Bruhat graph. - Eric W. Weisstein, Jul 29 2018

Examples

			(1!+2)/2 = 3/2 is not an integer.
a(2) = (2!+2)/2 = 2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 2..450
• Eric Weisstein's World of Mathematics, Bruhat Graph.
• Eric Weisstein's World of Mathematics, Clique.

Crossrefs

a(n) = (n!+m)/m: A038507 (m=1), this sequence (m=2), A139150 (m=3), A139151 (m=4), A139152 (m=5), A139153 (m=6), A139154 (m=7), A139155 (m=8), A139156 (m=9), A139157 (m=10).

Offsets for above sequences are Kempner numbers A002034.

For smallest number of the form (m!+n)/n see A139148.

Cf. A007749, A020458, A082672, A089085, A089130, A117141, A137390, A139056-A139066, A139068, A139070-A139075, A139157, A139159-A139162.

Programs

Mathematica

Table[(n! + 2)/2, {n, 2, 30}]

PARI

a(n)=n!/2+1 \\ Charles R Greathouse IV, Jun 20 2012