login
A157625
Product of the composite numbers between n+1 and 2n, both inclusive.
3
1, 4, 24, 48, 4320, 8640, 120960, 3628800, 7257600, 14515200, 6706022400, 13412044800, 8717829120000, 470762772480000, 941525544960000, 1883051089920000, 2112783322890240000, 147894832602316800000
OFFSET
1,2
COMMENTS
This function is very useful in a problem due to Paul Erdős recorded in A157017. - M. F. Hasler, Feb 26 2014
FORMULA
a(n) = n!*A000984(n)*A034386(n)/A034386(2n). - M. F. Hasler, Feb 26 2014
MATHEMATICA
nn=20; With[{comps=Complement[Range[2nn], Prime[Range[PrimePi[2nn]]]]}, Table[ Times@@ Select[comps, #>n&&#<=2n&], {n, nn}]] (* Harvey P. Dale, Feb 18 2013 *)
PROG
(PARI) a(n)=prod(i=n+1, 2*n, if(isprime(i), 1, i))
CROSSREFS
Cf. A073840, A157017, A144186 (product of primes between n+2 and 2n, both inclusive).
Sequence in context: A052645 A353250 A191778 * A128205 A085250 A166870
KEYWORD
nonn
AUTHOR
Jaume Oliver Lafont, Mar 03 2009
STATUS
approved