A189175 - OEIS

A189175

Riordan matrix (1+x/sqrt(1-4*x),(1-sqrt(1-4*x))/2).

1, 1, 1, 2, 2, 1, 6, 5, 3, 1, 20, 15, 9, 4, 1, 70, 49, 29, 14, 5, 1, 252, 168, 98, 49, 20, 6, 1, 924, 594, 342, 174, 76, 27, 7, 1, 3432, 2145, 1221, 627, 285, 111, 35, 8, 1, 12870, 7865, 4433, 2288, 1067, 440, 155, 44, 9, 1, 48620, 29172, 16302, 8437, 4004, 1716, 649, 209, 54, 10, 1

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OFFSET

0,4

COMMENTS

Row sums are A189176, diagonal sums are A189177.

LINKS

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

FORMULA

T(n,k)=[x^n] (1+x/sqrt(1-4*x))*((1-sqrt(1-4*x))/2)^k.

T(n,k) = binomial(2*n-k,n-k)*(n^2+n*k-k^2-k)/((2*n-k)*(2*n-k-1)) for k<=n, (n,k) <> (0,0), (1,1).

Recurrence: T(n+1,k+1) = T(n,k) + T(n,k+1) + ... + T(n,n).

EXAMPLE

Triangle begins:

1,1

2,2,1

6,5,3,1

20,15,9,4,1

70,49,29,14,5,1

252,168,98,49,20,6,1

924,594,342,174,76,27,7,1

3432,2145,1221,627,285,111,35,8,1

MATHEMATICA

T[n_, k_]=If[n==k, 1, Binomial[2n-k, n-k](n^2+n k-k^2-k)/((2n-k)(2n-k-1))]

Flatten[Table[T[n, k], {n, 0, 20}, {k, 0, n}]]

PROG

(Maxima) T(n, k):=if n=k then 1 else binomial(2*n-k, n-k)*(n^2+n*k-k^2-k)/((2*n-k)*(2*n-k-1));

create_list(T(n, k), n, 0, 20, k, 0, n);

CROSSREFS

Cf. A189176, A189177.

Sequence in context: A064784 A174302 A108074 * A271776 A171486 A127743

Adjacent sequences: A189172 A189173 A189174 * A189176 A189177 A189178

KEYWORD

nonn,easy,tabl

AUTHOR

Emanuele Munarini, Apr 18 2011

STATUS

approved