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A174266 Irregular triangle read by rows: T(n,k) = Sum_{i=0..k} (-1)^i * binomial(3*n+1,i) * binomial(k+3-i,3)^n, 0 <= k <= 3*(n-1). 15
1, 1, 9, 9, 1, 1, 54, 405, 760, 405, 54, 1, 1, 243, 6750, 49682, 128124, 128124, 49682, 6750, 243, 1, 1, 1008, 83736, 1722320, 12750255, 40241088, 58571184, 40241088, 12750255, 1722320, 83736, 1008, 1, 1, 4077, 922347, 45699447, 789300477, 5904797049, 21475242671 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

From Yahia Kahloune, Jan 30 2014: (Start)

In general, let b(k,e,p) = Sum_{i=0..k} (-1)^i*binomial(e*p+1,i)*binomial(k+e-i,e)^p. Then T(n,k) = b(k,3,n).

With these coefficients we can calculate: Sum_{i=1..n} binomial(i+e-1,e)^p = Sum_{i=0..e*(p-1)} b(i,e,p)*binomial(n+e+i,e*p+1).

For example, A086020(n) = Sum_{i=1..n} binomial(2+i, 3)^2 = T(2,0)*binomial(n+3, 7) + T(2,1)*binomial(n+4,7) + T(2,2)*binomial(n+5,7) + T(2,3)*binomial(n+6,7) = (1/5040)*(20*n^7 + 210*n^6 + 854*n^5 + 1680*n^4 + 1610*n^3 + 630*n^2 + 36*n).

(End)

T(n,k) is the number of permutations of 3 indistinguishable copies of 1..n with exactly k descents. A descent is a pair of adjacent elements with the second element less than the first. - Andrew Howroyd, May 06 2020

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..1335

FORMULA

T(n,k) = [x^k](1 - x)^(3*n + 1)*(Sum_{k>=0} (k*(k + 1)*(k - 1)/2)^n*x^k)/(3^n*x^2).

T(n,k) = T(n, 3*n-k).

From Yahia Kahloune, Jan 30 2014: (Start)

Sum_{i=1..n} binomial(2+i,3)^p = Sum_{i=0..3*p-3} T(p,i)*binomial(n+3+i,3*p+1).

binomial(n,3)^p = Sum_{i=0..3*p-3} T(p,i)*binomial(n+i,3*p). (End)

EXAMPLE

Triangle begins:

  1;

  1,      9,         9,            1;

  1,     54,       405,          760,            405,       54,        1;

  1,    243,      6750,        49682,         128124,   128124,    49682, ... ;

  1,   1008,     83736,      1722320,       12750255, 40241088, 58571184, ... ;

  1,   4077,    922347,     45699447,      789300477, ... ;

  1,  16362,   9639783,   1063783164,    38464072830, ... ;

  1,  65511,  98361900,  23119658500,  1641724670475, ... ;

  1, 262116, 992660346, 484099087156, 64856779908606, ... ;

...

The T(2,1) = 9 permutations of 111222 with 1 descent are: 112221, 112212, 112122, 122211, 122112, 121122, 222111, 221112, 211122. - Andrew Howroyd, May 07 2020

MATHEMATICA

p[x_, n_] = If[n == 0, 1, (1 - x)^(3*n + 1)*Sum[(k*( k + 1)*(2*k + 1)/6)^n*x^k, {k, 0, Infinity}]/x];

Table[CoefficientList[FullSimplify[ExpandAll[p[x, n]]], x], {n, 1, 10}];

Flatten[%]

PROG

(PARI) T(n, k)={sum(i=0, k, (-1)^i*binomial(3*n+1, i)*binomial(k+3-i, 3)^n)} \\ Andrew Howroyd, May 06 2020

CROSSREFS

Columns k=0..9 are A000012, A289254, A151632, A151633, A151634, A151635, A151636, A151637, A151638, A151639.

Row sums are A014606.

Similar triangles for e=1..6: A173018 (or A008292), A154283, this sequence, A236463, A237202, A237252.

Cf. A060187.

Sequence in context: A197350 A197364 A338217 * A334425 A280554 A195722

Adjacent sequences:  A174263 A174264 A174265 * A174267 A174268 A174269

KEYWORD

nonn,tabf

AUTHOR

Roger L. Bagula, Mar 14 2010

EXTENSIONS

Edited by Andrew Howroyd, May 06 2020

STATUS

approved

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Last modified March 5 04:24 EST 2021. Contains 341816 sequences. (Running on oeis4.)