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A119468 Triangle read by rows: T(n,k) = Sum_{j=0..n-k} binomial(n,2j)*binomial(n-2j,k). 8
1, 1, 1, 2, 2, 1, 4, 6, 3, 1, 8, 16, 12, 4, 1, 16, 40, 40, 20, 5, 1, 32, 96, 120, 80, 30, 6, 1, 64, 224, 336, 280, 140, 42, 7, 1, 128, 512, 896, 896, 560, 224, 56, 8, 1, 256, 1152, 2304, 2688, 2016, 1008, 336, 72, 9, 1, 512, 2560, 5760, 7680, 6720, 4032, 1680, 480, 90, 10, 1 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Product of Pascal's triangle A007318 and A119467. Row sums are A007051. Diagonal sums are A113225.

Variant of A080928, A115068 and A082137. - R. J. Mathar, Feb 09 2010

Matrix inverse of the Euler tangent triangle A081733. - Peter Luschny, Jul 18 2012

Central column: T(2*n,n) = A069723(n). - Peter Luschny, Jul 22 2012

Subtriangle of the triangle in A198792. - Philippe Deléham, Nov 10 2013

LINKS

Table of n, a(n) for n=0..65.

FORMULA

G.f.: (1 - x - xy)/(1 - 2x - 2x*y + 2x^2*y + x^2*y^2).

Number triangle T(n,k) = Sum_{j=0..n} binomial(n,j)*binomial(j,k)*(1+(-1)^(j-k))/2.

Define matrix: A(n,m,k) = If[m < n, 1, -1];

  p(x,k) = CharacteristicPolynomial[A[n,m,k],x]; then t(n,m) = coefficients(p(x,n)). - Roger L. Bagula and Gary W. Adamson, Jan 25 2009

E.g.f.: exp(x*z)/(1-tanh(x)). - Peter Luschny, Aug 01 2012

T(n,k) = 2*T(n-1,k) + 2*T(n-1,k-1) - 2*T(n-2,k-1) - T(n-2,k-2) for n >= 2, T(0,0) = T(1,0) = T(1,1) = 1, T(n,k) = 0 if k < 0 or if k > n. - Philippe Deléham, Nov 10 2013

E.g.f.: [(e^(2t)+1)/2] e^(tx) = e^(P.(x)t), so this is an Appell sequence with lowering operator D = d/dx and raising operator R = x + 2/(e^(-2D)+1), i.e., D P_n(x) = n P_{n-1}(x) and R p_n(x) = P_{n+1}(x) where P_n(x) = [(x+2)^n + x^n]/2. Also, (P.(x)+y)^n = P_n(x+y), umbrally. R = x + 1 + D - 2 D^3/3! + ... contains the e.g.f.(D) mod signs of A009006 and A155585 and signed, aerated A000182, the zag numbers, so the unsigned differential component 2/[e^(2D)+1] = 2 Sum_{n >= 0} Eta(-n) (-2D)^n/n!, where Eta(s) is the Dirichlet eta function, and 2 *(-2)^n Eta(-n) = (-1)^n (2^(n+1)-4^(n+1)) Zeta(-n) = (2^(n+1)-4^(n+1)) B(n+1)/(n+1) with Zeta(s), the Riemann zeta function, and B(n), the Bernoulli numbers. The polynomials PI_n(x) of A081733 are the umbral compositional inverses of this sequence, i.e., P_n(PI.(x)) = x^n = PI_n(P.(x)) under umbral composition. Aside from the signs and the main diagonals, multiplying this triangle by 2 gives the face-vectors of the hypercubes A038207. - Tom Copeland, Sep 27 2015

T(n,k) = 2^(n-k-1+0^(n-k))*binomial(n, k). - Peter Luschny, Nov 10 2017

EXAMPLE

Triangle begins

    1;

    1,    1;

    2,    2,    1;

    4,    6,    3,    1;

    8,   16,   12,    4,    1;

   16,   40,   40,   20,    5,    1;

   32,   96,  120,   80,   30,    6,    1;

   64,  224,  336,  280,  140,   42,    7,   1;

  128,  512,  896,  896,  560,  224,   56,   8,  1;

  256, 1152, 2304, 2688, 2016, 1008,  336,  72,  9,  1;

  512, 2560, 5760, 7680, 6720, 4032, 1680, 480, 90, 10, 1;

MAPLE

A119468_row := proc(n) local s, t, k;

  s := series(exp(z*x)/(1-tanh(x)), x, n+2);

  t := factorial(n)*coeff(s, x, n); seq(coeff(t, z, k), k=(0..n)) end:

for n from 0 to 7 do A119468_row(n) od; # Peter Luschny, Aug 01 2012

# Alternatively:

T := (n, k) -> 2^(n-k-1+0^(n-k))*binomial(n, k):

for n from 0 to 9 do seq(T(n, k), k=0..n) od; # Peter Luschny, Nov 10 2017

MATHEMATICA

A[k_] := Table[If[m < n, 1, -1], {m, k}, {n, k}]; a = Join[{{1}}, Table[(-1)^n*CoefficientList[CharacteristicPolynomial[A[n], x], x], {n, 1, 10}]]; Flatten[a] (* Roger L. Bagula and Gary W. Adamson, Jan 25 2009 *)

PROG

(Sage)

R = PolynomialRing(QQ, 'x')

def p(n, x) :

  return 1 if n==0 else add((-1)^n*binomial(n, k)*(x^(n-k)-1) for k in range(n))

def A119468_row(n) : return map(abs, R((p(n, x-1)-p(n, x+1))/2+x^n).coeffs())

for n in (0..8) : print A119468_row(n) # Peter Luschny, Jul 22 2012

CROSSREFS

A082137 read as triangle with rows reversed.

Cf. A000182, A009006, A038207, A081733, A155585.

Sequence in context: A273903 A080928 A068957 * A175136 A091869 A112307

Adjacent sequences:  A119465 A119466 A119467 * A119469 A119470 A119471

KEYWORD

easy,nonn,tabl

AUTHOR

Paul Barry, May 21 2006

STATUS

approved

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Last modified October 19 22:28 EDT 2018. Contains 316378 sequences. (Running on oeis4.)