A073840 Product of the composite numbers between n and 2n (both inclusive).

1, 4, 24, 192, 4320, 51840, 120960, 29030400, 65318400, 145152000, 6706022400, 160944537600, 8717829120000, 6590678814720000, 14122883174400000, 30128817438720000, 2112783322890240000, 2662106986841702400000

Offset

1,2

Comments

a(n) is divisible by central binomial coefficients, A001405[n]

Links

Table of n, a(n) for n=1..18.

Formula

a(n)=A049614(2n)/A049614(n-1)

Example

a(6) = 6*8*9*10*12 = 51840.

Maple

for n from 1 to 50 do l := 1:for j from n to 2*n do if not isprime(j) then l := l*j:fi:od:a[n] := l:od:seq(a[j], j=1..50);

Mathematica

cs[x_] := Flatten[Position[Table[PrimeQ[j], {j, x, 2*x}], False]]+x-1; prcs[x_] := Apply[Times, cs[x]]; Table[prcs[w], {w, 1, 25}]

Prog

(PARI) a(n)=prod(i=n, 2*n, i^if(isprime(i), 0, 1))

Crossrefs

Cf. A073839, A073641.

Sequence in context: A002866 A182798 A374852 * A024249 A007145 A241000

Adjacent sequences: A073837 A073838 A073839 * A073841 A073842 A073843

Keyword

nonn

Author

Amarnath Murthy, Aug 13 2002

Extensions

More terms from Sascha Kurz and Labos Elemer, Aug 14 2002

Status

approved