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 A125721 a(n)=2*n!/d(n!); d(m)=A000005(m) is the number of divisors of m. 0
 2, 2, 2, 3, 6, 15, 48, 168, 840, 4536, 26880, 147840, 1209600, 7862400, 67267200, 648648000, 7783776000, 66162096000, 871782912000, 8281937664000, 118562476032000, 1680623097753600, 23416681828700160, 269291841030051840, 5109094217170944000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(3)=3 and a(5)=15 are the only odd numbers in this sequence. REFERENCES P. Erdos, solved by J. Fiedler, Elem. Math. 16 (1961), 42-44, Aufgabe 374. LINKS FORMULA a(n)=2*A000142(n)/A027423(n). EXAMPLE a(4)=2*4!/d(4!)=2*24/8=6. MATHEMATICA Table[(2n!)/DivisorSigma[0, n!], {n, 0, 25}] (* Harvey P. Dale, Jun 01 2014 *) PROG (PARI) a(n) = 2*n!/numdiv(n!); \\ Michel Marcus, Aug 26 2013 CROSSREFS Cf. A000142, A027423. Sequence in context: A218694 A143596 A091712 * A049798 A165198 A245526 Adjacent sequences:  A125718 A125719 A125720 * A125722 A125723 A125724 KEYWORD nonn AUTHOR Franz Vrabec, Feb 01 2007 EXTENSIONS More terms from Michel Marcus, Aug 26 2013 STATUS approved

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Last modified August 7 17:44 EDT 2020. Contains 336278 sequences. (Running on oeis4.)