The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A014606 a(n) = (3n)!/(6^n). 38
 1, 1, 20, 1680, 369600, 168168000, 137225088000, 182509367040000, 369398958888960000, 1080491954750208000000, 4386797336285844480000000, 23934366266775567482880000000, 170891375144777551827763200000000, 1561776277448122046153927884800000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n) is also the constant term in the product : product 1 <= i,j <= n, i different from j (1 - x_i/x_j)^3. - Sharon Sela (sharonsela(AT)hotmail.com), Feb 14 2002 a(n) is also the number of n by 3n (0,1)-matrices with row sum 3 and column sum 1. In general, the number of n by sn(0,1)-matrices with row sum s and column sum 1 is ,(sn)!/(s!)^n). - Shanzhen Gao, Feb 12 2010 REFERENCES G. E. Andrews, R. Askey and R. Roy, Special Functions, Cambridge University Press, 1998. Gao, Shanzhen, and Matheis, Kenneth, Closed formulas and integer sequences arising from the enumeration of (0,1)-matrices with row sum two and some constant column sums. In Proceedings of the Forty-First Southeastern International Conference on Combinatorics, Graph Theory and Computing. Congr. Numer. 202 (2010), 45-53. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..165 J.-C. Novelli, J.-Y. Thibon, Hopf Algebras of m-permutations,(m+1)-ary trees, and m-parking functions, arXiv preprint arXiv:1403.5962 [math.CO], 2014-2020. FORMULA E.g.f. with interpolated zeros: 1/(1 - x^3/3!). - Geoffrey Critzer, Jun 07 2014 a(n) = A025035(n)*n! - Geoffrey Critzer, Jun 07 2014 a(n) = A089759(3,n). - R. J. Mathar, Nov 01 2015 MATHEMATICA nn=36; Select[Range[0, nn]!CoefficientList[Series[1/(1-x^3/3!), {x, 0, nn}], x], #>0&] (* Geoffrey Critzer, Jun 07 2014 *) PROG (PARI) a(n)=if(n<0, 0, (3*n)!/6^n) CROSSREFS Cf. A000680. Sequence in context: A177635 A177296 A177297 * A330196 A172556 A246619 Adjacent sequences:  A014603 A014604 A014605 * A014607 A014608 A014609 KEYWORD nonn,easy AUTHOR BjornE (mdeans(AT)algonet.se) 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
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 12 12:09 EDT 2020. Contains 336439 sequences. (Running on oeis4.)