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A109898 a(n) = least integer of the form (n-2)(n-4)...(n-2k)/n. 0 if no such number exists. 1

%I

%S 0,0,0,0,0,0,0,3,0,0,0,40,0,0,3003,105,0,71680,0,24192,2078505,0,0,

%T 330,4216455243,0,2788660875,39536640,0,256256,0,16380,6153560492625,

%U 0,276348105,15841280,0,0,20228646742486875,1116288,0,1190707200,0

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

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

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

%o (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

%Y Cf. A109899.

%K nonn

%O 1,8

%A _Amarnath Murthy_, Jul 13 2005

%E More terms from Matthew Conroy Mar 28 2006

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Last modified May 7 15:02 EDT 2021. Contains 343650 sequences. (Running on oeis4.)