A109898 a(n) is the least integer of the form (n-2)(n-4)...(n-2k)/n. 0 if no such number exists.

0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 40, 0, 0, 3003, 105, 0, 71680, 0, 24192, 2078505, 0, 0, 330, 4216455243, 0, 2788660875, 39536640, 0, 256256, 0, 16380, 6153560492625, 0, 276348105, 15841280, 0, 0, 20228646742486875, 1116288, 0, 1190707200, 0

Offset

1,8

Comments

a(n) = 0 if n = 1,9, p or 2*p, p is a prime. This is not exhaustive.

Links

Table of n, a(n) for n=1..43.

Example

a(12) = 10*8*6/12 = 40, a(15) = 13*11*9*7*5/15 = 3003.

Prog

(PARI) a(n) = pp=n-2; k=1; while((n-2*k>0) && ((pp % n)>0), k=k+1; pp=pp*(n-2*k)); if( ((pp%n)==0) && (pp>0), return(pp/n), return(0)); \\ Matthew Conroy, Mar 28 2006

Crossrefs

Cf. A109899.

Sequence in context: A007270 A222896 A057387 * A223074 A192732 A092573

Adjacent sequences: A109895 A109896 A109897 * A109899 A109900 A109901

Keyword

nonn

Author

Amarnath Murthy, Jul 13 2005

Extensions

More terms from Matthew Conroy, Mar 28 2006

Status

approved