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A136656
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Coefficients for rewriting generalized falling factorials into ordinary falling factorials.
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7
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1, 0, -2, 0, 6, 4, 0, -24, -36, -8, 0, 120, 300, 144, 16, 0, -720, -2640, -2040, -480, -32, 0, 5040, 25200, 27720, 10320, 1440, 64, 0, -40320, -262080, -383040, -199920, -43680, -4032, -128, 0, 362880, 2963520, 5503680, 3764880, 1142400, 163968, 10752, 256, 0, -3628800, -36288000, -82978560
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OFFSET
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0,3
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COMMENTS
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Generalization of (signed) Lah number triangle A008297 (amended with a trivial row n=0 and a column k=0 in order to have a Sheffer triangle structure of the Jabotinsky type).
product(s*t-j,j=0..n-1) := fallfac(s*t,n) (falling factorial with n factors) is called generalized factorial of t of order n and scale parameter s in the Charalambides reference p. 301 ch. 8.4.
The s-family of triangles L(s;n,k) (in the Charalambides reference called C(n,k;-s)) is defined for integer s by fallfac(-s*t,n) = ((-1)^n)*risefac(s*t,n) = sum(L(s;n,k)*fallfac(t,k),k=0..n), n>=0. risefac(x,n):=product(x+j,j=0..n-1) for the rising factorials.
For positive s the signless triangles |L(s;n,k)| = L(s;n,k)*(-1)^n satisfies risefac(s*t,n) = sum(|L(s;n,k)|*fallfac(t,k),k=0..n), n>=0.
For negative s see the combinatorial interpretation given in the Charalambides reference, Example 8.8, p. 313: Coupon collector's problem.
|T(n,k)| = B_{n,k}((j+2)!; j>=0) where B_{n,k} are the partial Bell polynomials. - Peter Luschny, May 11 2015
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REFERENCES
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Ch. A. Charalambides, Enumerative Combinatorics, Chapman & Hall/CRC, Boca Raton, Florida, 2002, ch. 8.4 p. 301 ff. Table 8.3 (with row n=0 and column k=0 and s=-2).
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LINKS
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FORMULA
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Recurrence: a(n,k) = 0 if n<k; a(n,0) = 1 if n=0 else 0 and a(n,k) = (-2*k-(n-1))*a(n-1,k)-2*a(n-1,k-1). From the Charalambides reference Theorem 8.19, p. 309, for s=-2.
E.g.f. column k: (1/(1+x)^2 - 1)^k/k!, k>=0. From the Charalambides reference Theorem 8.14, p. 305 for s=-2.(hence a Sheffer triangle of Jabotinsky type).
a(n,k) = sum(((-1)^(k-r))*binomial(k,r)*fallfac(-2*r,n),r=0..k)/k!, n>=k>=0. From the Charalambides reference Theorem 8.15, p. 306 for s=-2.
a(n,k) = sum(S1(n,r)*S2(r,k)*(-2)^r,r=k..n) with the Stirling numbers S1(n,r)= A048993(n,r) and S2(r,k)= A048993(r,k). From the Charalambides reference Theorem 8.13, p.304 for s=-2.
a(n,k) = sum(M_3(n,k,q)*product(fallfac(-2,j)^e(n,m,q,j),j=1..n),q=1..p(n,k)) if n>=k>=1, else 0. Here p(n,k)=A008284(n,m), the number of k parts partitions of n, the M_3 partition numbers are given in A036040 and e(n,m,q,j) is the exponent of j in the q-th k parts partition of n. Rewritten eq. (8.50), Theorem 8.16, p. 307, from the Charalambides reference for s=-2.
Recurrence for the unsigned case: a(n,k) = Sum_{j=0..n-k} a(n-j-1,k-1)*C(n-1,j)*(j+2)! if k<>0 else k^n. - Peter Luschny, Mar 31 2015
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EXAMPLE
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Triangle starts:
[1]
[0, -2]
[0, 6, 4]
[0, -24, -36, -8]
[0, 120, 300, 144, 16]
...
Recurrence: a(4,2) = -7*a(3,2)-2*a(3,1) = -7*(-36) -2*(-24) = 300.
a(4,2)=300 as sum over the M3 numbers A036040 for the 2 parts partitions of 4: 4*fallfac(-2,1)^1*fallfac(-2,3)^1 + 3*fallfac(-2,2)^2 = 4*(-2)*(-24)+3*6^2 = 300.
Row n=3: [0,-24,-36,-8] for the coefficients in rewriting fallfac(-2*t,3)=((-1)^3)*risefac(2*t,3) = ((-1)^3)*(2*t)*(2*t+1)*(2*t+2) = 0*1 -24*t -36*t*(t-1) -8*t*(t-1)*(t-2).
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MAPLE
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# The function BellMatrix is defined in A264428.
BellMatrix(n -> (-1)^(n+1)*(n+2)!, 9); # Peter Luschny, Jan 27 2016
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MATHEMATICA
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fallfac[n_, k_] := Pochhammer[n - k + 1, k]; a[n_, k_] := Sum[(-1)^(k - r)*Binomial[k, r]*fallfac[-2*r, n], {r, 0, k}]/k!; Table[a[n, k], {n, 0, 9}, {k, 0, n}] // Flatten (* Jean-François Alcover, Jul 09 2013 *)
BellMatrix[f_Function, len_] := With[{t = Array[f, len, 0]}, Table[BellY[n, k, t], {n, 0, len - 1}, {k, 0, len - 1}]];
rows = 10;
M = BellMatrix[(-1)^(# + 1)*(# + 2)!&, rows];
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PROG
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(Sage)
@CachedFunction
def T(n, k): # unsigned case
if k == 0: return 1 if n == 0 else 0
return sum(T(n-j-1, k-1)*(j+1)*(j+2)*gamma(n)/gamma(n-j) for j in (0..n-k))
for n in range(7): [T(n, k) for k in (0..n)] # Peter Luschny, Mar 31 2015
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CROSSREFS
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Cf. A136657 without row n=0 and column k=0, divided by 2.
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KEYWORD
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AUTHOR
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STATUS
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approved
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