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 A147630 a(1) = 1; for n>1, a(n) = Product_{k = 1..n-1} (9k - 3). 3
 1, 6, 90, 2160, 71280, 2993760, 152681760, 9160905600, 632102486400, 49303993939200, 4289447472710400, 411786957380198400, 43237630524920832000, 4929089879840974848000, 606278055220439906304000, 80028703289098067632128000, 11284047163762827536130048000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Original name was: 9-factorial numbers (5). LINKS FORMULA a(n+1) = Sum_{k, 0<=k<=n}A132393(n,k)*6^k*9^(n-k). - Philippe Deléham, Nov 09 2008 a(n) = n!*sum(k=1..n-1, binomial(k,n-k-1)*3^k*(-1)^(n-k-1)*binomial(n+k-1,n-1)))/n, also a(n) = n!*A097188(n). - Vladimir Kruchinin, Apr 01 2011 a(n) = (-3)^n*sum_{k=0..n} 3^k*s(n+1,n+1-k), where s(n,k) are the Stirling numbers of the first kind, A048994. - Mircea Merca, May 03 2012 a(n) = round(9^n * Gamma(n+6/9) / Gamma(6/9)). - Vincenzo Librandi, Feb 21 2015 MATHEMATICA s=1; lst={s}; Do[s+=n*s; AppendTo[lst, s], {n, 5, 2*5!, 9}]; lst Table[Product[9k-3, {k, 1, n-1}], {n, 20}] (* Harvey P. Dale, Sep 01 2016 *) PROG (Maxima) a(n):=n!*sum(binomial(k, n-k-1)*3^k*(-1)^(n-k-1)*binomial(n+k-1, n-1), k, 1, n-1))/n; /* Vladimir Kruchinin, Apr 01 2011 */ (MAGMA) [Round(9^n*Gamma(n+6/9)/Gamma(6/9)): n in [0..20]]; // Vincenzo Librandi, Feb 21 2015 (PARI) a(n) = n--; prod(k=1, n, 9*k-3); \\ Michel Marcus, Feb 28 2015 CROSSREFS Cf. A147629, A049211, A051232, A045756, A035012, A035013, A035017, A035018, A035020, A035022, A035023, A053116. Sequence in context: A266734 A004996 A001499 * A221097 A177584 A177558 Adjacent sequences:  A147627 A147628 A147629 * A147631 A147632 A147633 KEYWORD nonn,easy AUTHOR Vladimir Joseph Stephan Orlovsky, Nov 08 2008 EXTENSIONS New name from Peter Bala, Feb 20 2015 More terms from Michel Marcus, Feb 28 2015 STATUS approved

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Last modified June 27 16:21 EDT 2022. Contains 354896 sequences. (Running on oeis4.)