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 A005461 Number of simplices in barycentric subdivision of n-simplex. (Formerly M4985) 9
 1, 15, 180, 2100, 25200, 317520, 4233600, 59875200, 898128000, 14270256000, 239740300800, 4249941696000, 79332244992000, 1556132497920000, 32011868528640000, 689322235650048000, 15509750302126080000, 364022962973429760000, 8898339094906060800000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES R. Austin, R. K. Guy, and R. Nowakowski, unpublished notes, circa 1987. R. K. Guy, personal communication. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS G. C. Greubel, Table of n, a(n) for n = 1..440 R. Austin, R. K. Guy, & R. Nowakowski, Unpublished notes, 1987 Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets FORMULA a(n) = n*(n + 1)*(n + 3)!/48. Essentially Stirling numbers of second kind - see A028246. If we define f(n,i,x) = Sum_{k=i..n} Sum_{j=i..k} binomial(k,j)*Stirling1(n,k)*Stirling2(j,i)*x^(k-j) then a(n-3) = (-1)^n*f(n,4,-3), (n>=4). - Milan Janjic, Mar 01 2009 E.g.f.: t*(3*t + 2)/(2*(t - 1)^6). - Ran Pan, Jul 10 2016 a(n) ~ sqrt(Pi/2)*exp(-n)*n^(n+1/2)*(n^5/24 + 85*n^4/288 + 5065*n^3/6912 + 955841*n^2/1244160 + 3710929*n/11943936). - Ilya Gutkovskiy, Jul 10 2016 EXAMPLE G.f. = x + 15*x^2 + 180*x^3 + 2100*x^4 + 25200*x^5 + 317520*x^6 + ... MAPLE a:=n->sum((n-j)*n!/4!, j=3..n): seq(a(n), n=4..17); # Zerinvary Lajos, Apr 29 2007 MATHEMATICA Table[(n(n+1)(n+3)!)/48, {n, 20}] (* Harvey P. Dale, Mar 14 2012 *) a[ n_] := If[ n < 0, 0, n (n + 1) (n + 3)! / 48]; (* Michael Somos, May 27 2014 *) PROG (Sage) [factorial(m+1)*binomial(m-1, 2)/24 for m in range(3, 19)] # Zerinvary Lajos, Jul 05 2008 (Sage) [binomial(n, 4)*factorial (n-2)/2 for n in range(4, 18)] #  Zerinvary Lajos, Jul 07 2009 CROSSREFS Cf. A028246. Sequence in context: A293476 A004992 A055084 * A138443 A235455 A016158 Adjacent sequences:  A005458 A005459 A005460 * A005462 A005463 A005464 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from Harvey P. Dale, Mar 14 2012 STATUS approved

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Last modified January 28 01:38 EST 2021. Contains 340489 sequences. (Running on oeis4.)