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A098931
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a(0) = 1, a(n) = 1 + 2*3 + 4*5 + 6*7 + ... + (2n)*(2n+1) for n > 0.
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1
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1, 7, 27, 69, 141, 251, 407, 617, 889, 1231, 1651, 2157, 2757, 3459, 4271, 5201, 6257, 7447, 8779, 10261, 11901, 13707, 15687, 17849, 20201, 22751, 25507, 28477, 31669, 35091, 38751, 42657, 46817, 51239, 55931, 60901, 66157, 71707, 77559, 83721
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OFFSET
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0,2
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COMMENTS
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If a(n) = a0, a1, a2, a3, ... then Sum(a(n))= a0, a0+a1, a0+a1+a2, a0+a1+a2+a3, ...
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LINKS
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FORMULA
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a(n) = 1 + 3*n^2 + n*(5 + 4*n^2)/3.
G.f.: (1 + 3*x + 5*x^2 - x^3)/(1-x)^4.
E.g.f.: (1+6*x+7*x^2+(4/3)*x^3)*exp(x).
a(n) = 1 + Sum(A068377(i),i=1..n+1). (End)
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EXAMPLE
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a(0) = 1;
a(1) = 1 + 2*3 = 7;
a(2) = 1 + 2*3 + 4*5 = 27, etc.
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MAPLE
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seq((4/3)*n^3+3*n^2+(5/3)*n+1, n=0..100); # Robert Israel, Jul 28 2015
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MATHEMATICA
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LinearRecurrence[{4, -6, 4, -1}, {1, 7, 27, 69}, 40] (* Vincenzo Librandi, Jul 28 2015 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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