A002691 -id:A002691 - cp's OEIS frontend

A133399 Triangle T(n,k)=number of forests of labeled rooted trees with n nodes, containing exactly k trees of height one, all others having height zero (n>=0, 0<=k<=floor(n/2)).

1, 1, 1, 2, 1, 9, 1, 28, 12, 1, 75, 120, 1, 186, 750, 120, 1, 441, 3780, 2100, 1, 1016, 16856, 21840, 1680, 1, 2295, 69552, 176400, 45360, 1, 5110, 272250, 1224720, 705600, 30240, 1, 11253, 1026300, 7692300, 8316000, 1164240, 1, 24564, 3762132, 45018600

Offset: 0

Alois P. Heinz, Nov 24 2007

			Triangle begins:
  1;
  1;
  1,     2;
  1,     9;
  1,    28,     12;
  1,    75,    120;
  1,   186,    750,     120;
  1,   441,   3780,    2100;
  1,  1016,  16856,   21840,   1680;
  1,  2295,  69552,  176400,  45360;
  1,  5110, 272250, 1224720, 705600, 30240;
  ...

Alois P. Heinz, Rows n = 0..200, flattened
A. P. Heinz, Finding Two-Tree-Factor Elements of Tableau-Defined Monoids in Time O(n^3), Ed. S. G. Akl, F. Fiala, W. W. Koczkodaj: Advances in Computing and Information, ICCI90 Niagara Falls, LNCS 468, Springer-Verlag (1990), pp. 120-128.

Columns k=1,2 give: A058877, A133386.
Row sums give: A000248.
T(2n,n) = A001813(n), T(2n+1,n) = A002691(n).
Reading the table by diagonals gives triangle A198204. - Peter Bala, Jul 31 2012
Cf. A235596.

/* As triangle */ [[Binomial(n,k)*Factorial(k)*StirlingSecond(n-k+1,k+1): k in [0..Floor(n/2)]]: n in [0.. 15]]; // Vincenzo Librandi, Jun 06 2019

T:= (n,k)-> binomial(n,k)*k!*Stirling2(n-k+1,k+1): for n from 0 to 10 do lprint(seq(T(n, k), k=0..floor(n/2))) od;

nn=12;f[list_]:=Select[list,#>0&];Map[f,Range[0,nn]!CoefficientList[ Series[Exp[y x (Exp[x]-1)] Exp[x],{x,0,nn}],{x,y}]]//Grid (* Geoffrey Critzer, Feb 09 2013 *)
t[n_, k_] := Binomial[n, k]*k!*StirlingS2[n-k+1, k+1]; Table[t[n, k], {n, 0, 12}, {k, 0, n/2}] // Flatten (* Jean-François Alcover, Dec 19 2013 *)

T(n,k) = C(n,k) * k! * stirling2(n-k+1,k+1).
E.g.f.: exp(y*x*(exp(x)-1))*exp(x). - Geoffrey Critzer, Feb 09 2013
Sum_{k=1..floor(n/2)} T(n,k) = A235596(n+1). - Alois P. Heinz, Jun 21 2019

A198204 Series reversion of (1 - tx)log(1 + x) with respect to x.

Original entry on oeis.org

1, 1, 2, 1, 9, 12, 1, 28, 120, 120, 1, 75, 750, 2100, 1680, 1, 186, 3780, 21840, 45360, 30240, 1, 441, 16856, 176400, 705600, 1164240, 665280, 1, 1016, 69552, 1224720, 8316000, 25280640, 34594560, 17297280, 1, 2295, 272250, 7692300, 82577880, 408648240, 998917920, 1167566400, 518918400

Offset: 1

Peter Bala, Jul 31 2012

This triangle is A133399 read by diagonals.

			Triangle begins
.n\k.|..0....1.....2......3......4......5
= = = = = = = = = = = = = = = = = = = = =
..1..|..1
..2..|..1....2
..3..|..1....9....12
..4..|..1...28...120....120
..5..|..1...75...750...2100...1680
..6..|..1..186..3780..21840..45360..30240
...

Cf. A001813, A002691, A052892, A058877, A133386, A133399, A141618.

Flatten[CoefficientList[CoefficientList[InverseSeries[Series[Log[1 + x]*(1 - t*x),{x,0,9}]], x]*Table[n!, {n,0,9}], t]] (* Peter Luschny, Oct 25 2015 *)

T(n,k) = k!*binomial(n + k - 1,k)*Stirling2(n,k + 1) (n >= 1, k >=0).
E.g.f.: A(x,t) = series reversion of (1 - t*x)*log(1 + x) w.r.t. x = x + (1 + 2*t)*x^2/2! + (1 + 9*t + 12*t^2)*x^3/3! + ....
Main diagonal A001813, first subdiagonal A002691.
Column 1 A058877, column 2 A133386. Row sums A052892.
1 - t*A(x,t) = x/series reversion of x*(1 - t(exp(x) - 1)) with respect to x. Cf. A141618. - Peter Bala, Oct 22 2015

A002690 a(n) = (n+1) * (2*n)! / n!.

Original entry on oeis.org

1, 4, 36, 480, 8400, 181440, 4656960, 138378240, 4670265600, 176432256000, 7374868300800, 337903056691200, 16838835658444800, 906706535454720000, 52459449551308800000, 3245491278907637760000, 213796737998040637440000, 14940619102451310428160000, 1103945744792235714969600000

Offset: 0

N. J. A. Sloane

Coefficients of orthogonal polynomials.
E.g.f. for series with alternating signs: x/(1+4*x)^(1/2).
Central terms of triangle A245334. - Reinhard Zumkeller, Aug 30 2014

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Vincenzo Librandi, Table of n, a(n) for n = 0..200
H. E. Salzer, Orthogonal polynomials arising in the evaluation of inverse Laplace transforms, Math. Comp. 9 (1955), 164-177.
H. E. Salzer, Orthogonal polynomials arising in the evaluation of inverse Laplace transforms, Math. Comp. 9 (1955), 164-177. [Annotated scanned copy]

a(n) = (n+1) * A001813(n) = 2^n * A001193(n+1).
Cf. A002691, A000407.
Cf. A245334.

a002690 n = a245334 (2 * n) n  -- Reinhard Zumkeller, Aug 30 2014

[(n+1) * Factorial(2*n) /Factorial(n): n in [0..20]]; // Vincenzo Librandi, Sep 05 2011

with(combstruct):bin := {B=Union(Z,Prod(B,B))}:
seq (count([B,bin,labeled],size=n+1)*(n+1), n=0..17); # Zerinvary Lajos, Dec 05 2007
A002690 := n -> 2^n*n!*JacobiP(n, -1/2, -n+1, 3):
seq(simplify(A002690(n)), n = 0..18);  # Peter Luschny, Jan 22 2025

Table[((n+1)(2n)!)/n!,{n,0,20}] (* Harvey P. Dale, Sep 04 2011 *)

PARI
```
a(n)=(n+1)*(2*n)!/n!
```

E.g.f.: (1-2*x)/(1-4*x)^(3/2).

a(n) = 2^n*n!*JacobiP(n, -1/2, -n+1, 3). - Peter Luschny, Jan 22 2025

Edited by Ralf Stephan, Mar 21 2004

A278071 Triangle read by rows, coefficients of the polynomials P(n,x) = (-1)^n*hypergeom( [n,-n], [], x), powers in descending order.

Original entry on oeis.org

1, 1, -1, 6, -4, 1, 60, -36, 9, -1, 840, -480, 120, -16, 1, 15120, -8400, 2100, -300, 25, -1, 332640, -181440, 45360, -6720, 630, -36, 1, 8648640, -4656960, 1164240, -176400, 17640, -1176, 49, -1, 259459200, -138378240, 34594560, -5322240, 554400, -40320, 2016, -64, 1

Offset: 0

Peter Luschny, Nov 10 2016

			Triangle starts:
.       1,
.       1,      -1,
.       6,      -4,     1,
.      60,     -36,     9,    -1,
.     840,    -480,   120,   -16,   1,
.   15120,   -8400,  2100,  -300,  25,  -1,
.  332640, -181440, 45360, -6720, 630, -36, 1,
...

H. L. Krall and O. Fink, A New Class of Orthogonal Polynomials: The Bessel Polynomials, Trans. Amer. Math. Soc. 65, 100-115, 1949.
Herbert E. Salzer, Orthogonal Polynomials Arising in the Numerical Evaluation of Inverse Laplace Transforms, Mathematical Tables and Other Aids to Computation, Vol. 9, No. 52 (Oct., 1955), pp. 164-177, (see p.174 and footnote 7).

Cf. A278069 (x=1, row sums up to sign), A278070 (x=-1).
T(n,0) = Pochhammer(n, n) (cf. A000407).
T(n,1) = -(n+1)*(2n)!/n! (cf. A002690).
T(n,2) = (n+2)*(2n+1)*(2n-1)!/(n-1)! (cf. A002691).
T(n,n-1) = (-1)^(n+1)*n^2 for n>=1 (cf. A000290).
T(n,n-2) = n^2*(n^2-1)/2 for n>=2 (cf. A083374).

p := n -> (-1)^n*hypergeom([n, -n], [], x):
ListTools:-Flatten([seq(PolynomialTools:-CoefficientList(simplify(p(n)), x, termorder=reverse), n=0..8)]);
# Alternatively the polynomials by recurrence:
P := proc(n,x) if n=0 then return 1 fi; if n=1 then return x-1 fi;
((((4*n-2)*(2*n-3)*x+2)*P(n-1,x)+(2*n-1)*P(n-2,x))/(2*n-3));
sort(expand(%)) end: for n from 0 to 6 do lprint(P(n,x)) od;
# Or by generalized Laguerre polynomials:
P := (n,x) -> n!*(-x)^n*LaguerreL(n,-2*n,-1/x):
for n from 0 to 6 do simplify(P(n,x)) od;

row[n_] := CoefficientList[(-1)^n HypergeometricPFQ[{n, -n}, {}, x], x] // Reverse;
Table[row[n], {n, 0, 8}] // Flatten (* Jean-François Alcover, Jul 12 2019 *)
(* T(n,k)= *) t={};For[n=8,n>-1,n--,For[j=n+1,j>0,j--,PrependTo[t,(-1)^(j-n+1-Mod[n,2])*Product[(2*n-k)*k/(n-k+1),{k,j,n}]]]];t (* Detlef Meya, Aug 02 2023 *)

The P(n,x) are orthogonal polynomials. They satisfy the recurrence
P(n,x) = ((((4*n-2)*(2*n-3)*x+2)*P(n-1,x)+(2*n-1)*P(n-2,x))/(2*n-3)) for n>=2.
In terms of generalized Laguerre polynomials (see the Krall and Fink link):
P(n,x) = n!*(-x)^n*LaguerreL(n,-2*n,-1/x).

cp's OEIS Frontend

A133399 Triangle T(n,k)=number of forests of labeled rooted trees with n nodes, containing exactly k trees of height one, all others having height zero (n>=0, 0<=k<=floor(n/2)).

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A198204 Series reversion of (1 - t*x)*log(1 + x) with respect to x.

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A002690 a(n) = (n+1) * (2*n)! / n!.

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A278071 Triangle read by rows, coefficients of the polynomials P(n,x) = (-1)^n*hypergeom( [n,-n], [], x), powers in descending order.

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A198204 Series reversion of (1 - tx)log(1 + x) with respect to x.