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 A004747 Triangle read by rows: the Bell transform of the triple factorial numbers A008544 without column 0. 15
 1, 2, 1, 10, 6, 1, 80, 52, 12, 1, 880, 600, 160, 20, 1, 12320, 8680, 2520, 380, 30, 1, 209440, 151200, 46480, 7840, 770, 42, 1, 4188800, 3082240, 987840, 179760, 20160, 1400, 56, 1, 96342400, 71998080, 23826880, 4583040, 562800, 45360, 2352, 72, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Previous name was: Triangle of numbers related to triangle A048966; generalization of Stirling numbers of second kind A008277, Bessel triangle A001497. a(n,m) := S2p(-2; n,m), a member of a sequence of triangles including S2p(-1; n,m) := A001497(n-1,m-1) (Bessel triangle) and ((-1)^(n-m))*S2p(1; n,m) := A008277(n,m) (Stirling 2nd kind). a(n,1)= A008544(n-1). a(n,m), n>=m>=1, enumerates unordered n-vertex m-forests composed of m plane (aka ordered) increasing (rooted) trees where vertices of out-degree r>=0 come in r+1 different types (like an (r+1)-ary vertex). Proof from the e.g.f. of the first column Y(z):=1-(1-3*x)^(1/3) and the F. Bergeron et al. eq. (8) Y'(z)= phi(Y(z)), Y(0)=0, with out-degree o.g.f. phi(w)=1/(1-w)^2. - Wolfdieter Lang, Oct 12 2007 Also the Bell transform of the triple factorial numbers A008544 which adds a first column (1,0,0 ...) on the left side of the triangle. For the definition of the Bell transform see A264428. See A051141 for the triple factorial numbers A032031 and A203412 for the triple factorial numbers A007559 as well as A039683 and A132062 for the case of double factorial numbers. - Peter Luschny, Dec 21 2015 LINKS F. Bergeron, Ph. Flajolet and B. Salvy, Varieties of increasing trees, Lecture Notes in Computer Science vol. 581, ed. J.-C. Raoult, Springer 1992, pp. 24-48. P. Blasiak, K. A. Penson and A. I. Solomon, The general boson normal ordering problem, arXiv:quant-ph/0402027, 2004. Richell O. Celeste, Roberto B. Corcino, Ken Joffaniel M. Gonzales. Two Approaches to Normal Order Coefficients. Journal of Integer Sequences, Vol. 20 (2017), Article 17.3.5. M. Janjic, Some classes of numbers and derivatives, JIS 12 (2009) 09.8.3 Wolfdieter Lang, On generalizations of Stirling number triangles, J. Integer Seqs., Vol. 3 (2000), #00.2.4. Wolfdieter Lang, Combinatorial Interpretation of Generalized Stirling Numbers, J. Int. Seqs. Vol. 12 (2009) 09.3.3. FORMULA a(n, m) = n!*A048966(n, m)/(m!*3^(n-m)); a(n+1, m) = (3*n-m)*a(n, m)+ a(n, m-1), n >= m >= 1; a(n, m) := 0, n 3^n/m!*(1/3*m*GAMMA(n-1/3)*hypergeom([1-1/3*m, 2/3-1/3*m, 1/3-1/3*m], [2/3, 4/3-n], 1)/GAMMA(2/3)-1/6*m*(m-1)*GAMMA(n-2/3)*hypergeom( [1-1/3*m, 2/3-1/3*m, 4/3-1/3*m], [4/3, 5/3-n], 1)/Pi*3^(1/2)*GAMMA(2/3)): for n from 1 to 6 do seq(simplify(a(n, k)), k=1..n) od; # Karol A. Penson, Feb 06 2004 # The function BellMatrix is defined in A264428. # Adds (1, 0, 0, 0, ..) as column 0. BellMatrix(n -> mul(3*k+2, k=(0..n-1)), 9); # Peter Luschny, Jan 29 2016 MATHEMATICA a[1, 1] = 1; a[_, 0] = 0; a[0, _] = 0; a[n_, m_] := (3*(n-1) - m)*a[n-1, m] + a[n-1, m-1]; Flatten[Table[a[n, m], {n, 1, 9}, {m, 1, n}] ][[1 ;; 45]] (* Jean-François Alcover, Jun 16 2011, after recurrence *) f[n_, m_] := m/n Sum[Binomial[k, n - m - k] 3^k (-1)^(n - m - k) Binomial[n + k - 1, n - 1], {k, 0, n - m}]; Table[n! f[n, m]/(m! 3^(n - m)), {n, 9}, {m, n}] // Flatten (* Michael De Vlieger, Dec 23 2015 *) rows = 9; a[n_, m_] := BellY[n, m, Table[Product[3k+2, {k, 0, j-1}], {j, 0, rows}]]; Table[a[n, m], {n, 1, rows}, {m, 1, n}] // Flatten (* Jean-François Alcover, Jun 22 2018 *) PROG (Sage) # The function bell_transform is defined in A264428. triplefactorial = lambda n: prod(3*k+2 for k in (0..n-1)) def A004747_row(n):     trifact = [triplefactorial(k) for k in (0..n)]     return bell_transform(n, trifact) [A004747_row(n) for n in (0..10)] # Peter Luschny, Dec 21 2015 CROSSREFS Row sums give A015735. Cf. A001497, A008277, A008544, A048966. Cf. A007559, A008544, A032031, A039683, A051141, A132062, A203412, A264428. Sequence in context: A193900 A319373 A143172 * A155810 A225470 A081099 Adjacent sequences:  A004744 A004745 A004746 * A004748 A004749 A004750 KEYWORD easy,nonn,tabl AUTHOR EXTENSIONS New name from Peter Luschny, Dec 21 2015 STATUS approved

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Last modified March 24 11:46 EDT 2019. Contains 321448 sequences. (Running on oeis4.)