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A174266
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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).
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15
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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
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OFFSET
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1,3
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COMMENTS
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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
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LINKS
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Andrew Howroyd, Table of n, a(n) for n = 1..1335
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FORMULA
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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)
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EXAMPLE
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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
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MATHEMATICA
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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[%]
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PROG
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(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
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CROSSREFS
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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
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KEYWORD
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nonn,tabf
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AUTHOR
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Roger L. Bagula, Mar 14 2010
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EXTENSIONS
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Edited by Andrew Howroyd, May 06 2020
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STATUS
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approved
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