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A016946
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a(n) = (6*n+3)^2.
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14
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9, 81, 225, 441, 729, 1089, 1521, 2025, 2601, 3249, 3969, 4761, 5625, 6561, 7569, 8649, 9801, 11025, 12321, 13689, 15129, 16641, 18225, 19881, 21609, 23409, 25281, 27225, 29241, 31329, 33489, 35721, 38025, 40401, 42849, 45369, 47961, 50625, 53361, 56169
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OFFSET
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0,1
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LINKS
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FORMULA
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G.f.: 9*(1+6*x+x^2)/(1-x)^3.
a(n) = 3*a(n-1)-3*a(n-2)+a(n-3).
Sum_{n>=0} (-1)^n/a(n) = G/9, where G is Catalan's constant (A006752). - Amiram Eldar, Mar 30 2022
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MAPLE
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MATHEMATICA
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(6 Range[0, 50] + 3)^2 (* or *)
CoefficientList[Series[9 (1 + 6 x + x^2)/(1 - x)^3, {x, 0, 50}], x] (* Wesley Ivan Hurt, Oct 13 2014 *)
LinearRecurrence[{3, -3, 1}, {9, 81, 225}, 40] (* Harvey P. Dale, Jul 13 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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STATUS
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approved
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