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A133367
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Triangle T(n,k) read by rows given by [2,1,2,1,2,1,2,1,2,1,2,1,...] DELTA [1,0,0,0,0,0,0,0,...] where DELTA is the operator defined in A084938 .
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1
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1, 2, 1, 6, 5, 1, 22, 23, 8, 1, 90, 107, 49, 11, 1, 394, 509, 276, 84, 14, 1, 1806, 2473, 1505, 556, 128, 17, 1, 8558, 12235, 8100, 3429, 974, 181, 20, 1, 41586, 61463, 43393, 20355, 6713, 1557, 243, 23, 1
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OFFSET
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0,2
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COMMENTS
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Riordan array ((1-x-sqrt(1-6x+x^2))/(2x), (1-3x-sqrt(1-6x+x^2))/(4x)).
Inverse of Riordan array (1/(1+2x),x/(1+3x+2x^2)) (a signed version of A124237). Paul Barry, Apr 28 2009:
Peart and Woodson give a factorization of this array in the Riordan group as (1/(1 - 3*x), x/(1 - 3*x)) * (C(2*x^2), x*C(2*x^2)) * (1/(1 + x), x), where C(x) = 1 + x + 2*x^2 + 5*x^3 + 14*x^4 + ... is the o.g.f. of the Catalan numbers A000108. - Peter Bala, Aug 07 2014
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LINKS
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FORMULA
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T(0,0)=1 ; T(n,k)=0 if k<0 or if k>n ; T(n,0) = 2*T(n-1,0)+2*T(n-1,1) ; T(n,k) = T(n-1,k-1)+3*T(n-1,k)+2*T(n-1,k+1) for k>=1 .
G.f.: 1/(1-xy-2x-x^2(2+y)/(1-3x-2x^2/(1-3x-2x^2/(1-3x-2x^2/(1- ... (continued fraction). - Paul Barry, Apr 28 2009
T(n,k) = S(n,n-k) - 2*S(n, n-k-2), where S(n,k) = Sum_{j = 0..k} binomial(n-1,k-j)*binomial(n,j)*2^j. - Peter Bala, Feb 20 2018
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EXAMPLE
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Triangle begins
1,
2, 1,
6, 5, 1,
22, 23, 8, 1,
90, 107, 49, 11, 1,
394, 509, 276, 84, 14, 1,
1806, 2473, 1505, 556, 128, 17, 1
Production matrix begins
2, 1,
2, 3, 1,
0, 2, 3, 1,
0, 0, 2, 3, 1,
0, 0, 0, 2, 3, 1,
0, 0, 0, 0, 2, 3, 1,
0, 0, 0, 0, 0, 2, 3, 1; (End)
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MAPLE
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S := proc (n, k)
add(binomial(n-1, k-j)*binomial(n, j)*2^j, j = 0..k);
end proc:
for n from 0 to 10 do
seq(S(n, n-k)-2*S(n, n-k-2), k = 0..n)
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MATHEMATICA
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T[n_, 0] := Hypergeometric2F1[-n, n + 1, 2, -1]; T[n_, k_] := Binomial[-1 + n, -k + n] Hypergeometric2F1[k - n, -n, k, 2] - 2 Binomial[-1 + n, -2 - k + n] Hypergeometric2F1[2 + k - n, -n, 2 + k, 2]; Table[T[n, k], {n, 0, 8}, {k, 0, n}] // Flatten (* Peter Luschny, Feb 20 2018 *)
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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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