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A127893
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Riordan array (1/(1-x)^3, x/(1-x)^3).
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7
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1, 3, 1, 6, 6, 1, 10, 21, 9, 1, 15, 56, 45, 12, 1, 21, 126, 165, 78, 15, 1, 28, 252, 495, 364, 120, 18, 1, 36, 462, 1287, 1365, 680, 171, 21, 1, 45, 792, 3003, 4368, 3060, 1140, 231, 24, 1, 55, 1287, 6435, 12376, 11628, 5985, 1771, 300, 27, 1
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OFFSET
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0,2
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COMMENTS
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Let M denote the unsigned version of the lower unit triangular array A122432 and for k = 0,1,2,... define M(k) to be the lower unit triangular block array
/I_k 0\
\ 0 M/
having the k x k identity matrix I_k as the upper left block; in particular, M(0) = M. Then the present triangle equals the infinite matrix product M(0)*M(1)*M(2)*... (which is clearly well-defined). See the Example section. (End)
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LINKS
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FORMULA
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T(n,k) = binomial(n+2*k+2, n-k).
Sum_{k=0..n} T(n, k) = A052529(n+1) (row sums).
Sum_{k=0..floor(n/2)} T(n-k, k) = A095263(n+1) (diagonal sums).
Recurrence: T(n+1, k+1) = Sum_{i = 0..n-k} binomial(i+2, 2)*T(n-i,k). - Peter Bala, Jul 22 2014
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EXAMPLE
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Triangle begins
1;
3, 1;
6, 6, 1;
10, 21, 9, 1;
15, 56, 45, 12, 1;
21, 126, 165, 78, 15, 1;
28, 252, 495, 364, 120, 18, 1;
36, 462, 1287, 1365, 680, 171, 21, 1;
45, 792, 3003, 4368, 3060, 1140, 231, 24, 1;
55, 1287, 6435, 12376, 11628, 5985, 1771, 300, 27, 1;
66, 2002, 12870, 31824, 38760, 26334, 10626, 2600, 378, 30, 1;
...
With the arrays M(k) as defined in the Comments section, the infinite product M(0*)M(1)*M(2)*... begins
/ 1 \/1 \/1 \ / 1 \
| 3 1 ||0 1 ||0 1 | | 3 1 |
| 6 3 1 ||0 3 1 ||0 0 1 |... = | 6 6 1 |
|10 6 3 1 ||0 6 3 1 ||0 0 3 1 | |10 21 9 1|
|15 10 6 3 1||0 10 6 3 1||0 0 6 3 1| |... |
|... ||... ||... | |... |
(End)
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MAPLE
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seq(seq(binomial(n+2*k+2, n-k), k=0..n), n=0..10); # Robert Israel, Apr 28 2015
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MATHEMATICA
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Flatten@ Table[Binomial[n+2k-1, n-k], {n, 10}, {k, n}] (* Michael De Vlieger, Apr 27 2015 *)
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PROG
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(PARI) for(n=0, 10, for(k=0, n, print1(binomial(n+2*k+2, n-k), ", "))) \\ G. C. Greubel, Apr 29 2018
(Magma) [Binomial(n+2*k+2, n-k): k in [0..n], n in [0..10]]; // G. C. Greubel, Apr 29 2018
(GAP) Flat(List([0..10], n->List([0..n], k->Binomial(n+2*k+2, n-k)))); # Muniru A Asiru, Apr 30 2018
(Sage) flatten([[binomial(n+2*k+2, n-k) for k in (0..n)] for n in (0..12)]) # G. C. Greubel, Apr 16 2021
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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