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A033487
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a(n) = n*(n+1)*(n+2)*(n+3)/4.
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23
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0, 6, 30, 90, 210, 420, 756, 1260, 1980, 2970, 4290, 6006, 8190, 10920, 14280, 18360, 23256, 29070, 35910, 43890, 53130, 63756, 75900, 89700, 105300, 122850, 142506, 164430, 188790, 215760, 245520, 278256, 314160, 353430, 396270, 442890, 493506
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OFFSET
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0,2
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COMMENTS
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Non-vanishing diagonal of A132440^4/4. Third subdiagonal of unsigned A238363 without the zero. Cf. A130534 for relations to colored forests, disposition of flags on flagpoles, and colorings of the vertices of the complete graph K_4. - Tom Copeland, Apr 05 2014
Total number of pips on a set of trominoes (3-armed dominoes) with up to n pips on each arm. - Alan Shore and N. J. A. Sloane, Jan 06 2016
Also the number of minimum connected dominating sets in the (n+2)-crown graph. - Eric W. Weisstein, Jun 29 2017
Crossing number of the (n+3)-cocktail party graph (conjectured). - Eric W. Weisstein, Apr 29 2019
Sum of all numbers in ordered triples (x,y,z) where 0 <= x <= y <= z <= n. - Edward Krogius, Jul 31 2022
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REFERENCES
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J. Riordan, Combinatorial Identities, Wiley, 1968, p. 77.
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LINKS
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FORMULA
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From Antonio G. Astudillo (afg_astudillo(AT)hotmail.com), Jun 10 2001: (Start)
G.f.: -6*x/(x-1)^5.
a(n) = 6*binomial(n+3, 4) = a(n-1) + A007531(n+1) = 6*A000332(n) = Sum_{i=0..n} i*(i+1)*(i+2). (End)
Constant term in Bessel polynomial {y_n(x)}''.
a(n-1) = Sum_{j=1..n} Sum_{i=2..n} i*j = Sum_{j=1..n} j*(n+2)*(n-1)/2. - Zerinvary Lajos, May 11 2007
a(-3-n) = a(n) = 2 * binomial(binomial(n+2, 2), 2). - Michael Somos, Apr 06 2014
Sum_{n>=1} (-1)^(n+1)/a(n) = 16*log(2)/3 - 32/9. - Amiram Eldar, Nov 02 2021
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EXAMPLE
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G.f. = 6*x + 30*x^2 + 90*x^3 + 210*x^4 + 420*x^5 + 756*x^6 + 1260*x^7 + ...
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MAPLE
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MATHEMATICA
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Table[Times @@ (n + Range[0, 3])/4, {n, 0, 40}] (* Harvey P. Dale, Nov 27 2013 *)
LinearRecurrence[{5, -10, 10, -5, 1}, {0, 6, 30, 90, 210}, 40] (* Harvey P. Dale, Nov 27 2013 *)
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PROG
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(PARI) concat(0, Vec(-6*x/(x-1)^5 + O(x^100))) \\ Altug Alkan, Nov 29 2015
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CROSSREFS
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A column of the triangle in A331430.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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