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A073840 Product of the composite numbers between n and 2n (both inclusive). 2
1, 4, 24, 192, 4320, 51840, 120960, 29030400, 65318400, 145152000, 6706022400, 160944537600, 8717829120000, 6590678814720000, 14122883174400000, 30128817438720000, 2112783322890240000, 2662106986841702400000 (list; graph; refs; listen; history; text; internal format)
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: A293021 A002866 A182798 * 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

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Last modified November 27 11:07 EST 2022. Contains 358395 sequences. (Running on oeis4.)