login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Table of n, a(n) for n=1..17.

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 by Peter Bala, Feb 20 2015

More terms from Michel Marcus, Feb 28 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified June 28 17:16 EDT 2017. Contains 288839 sequences.