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A134965
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a(1)=3, a(n) = a(n-1) + 7 + 2*mod(n-1, 2) for n>=2.
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1
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3, 12, 19, 28, 35, 44, 51, 60, 67, 76, 83, 92, 99, 108, 115, 124, 131, 140, 147, 156, 163, 172, 179, 188, 195, 204, 211, 220, 227, 236, 243, 252, 259, 268, 275, 284, 291, 300, 307, 316, 323, 332, 339, 348, 355, 364, 371, 380, 387, 396, 403, 412, 419, 428
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OFFSET
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1,1
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COMMENTS
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Starting weights for pyramid game.
Numbers n such that the equation m(m + 1)/2 + 1 - n == 0 mod m has a solution.
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LINKS
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FORMULA
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G.f.: (3+9*x+4*x^2)/((1-x)^2*(x+1)).
(End)
a(n) = 8*n - 4 for n even.
a(n) = 8*n - 5 for n odd.
a(n) = a(n-1) + a(n-2) - a(n-3) for n>3.
(End)
E.g.f.: 4 + ((16*x - 9)*exp(x) + exp(-x))/2. - David Lovler, Aug 21 2022
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MATHEMATICA
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Flatten[Table[If[ IntegerQ[2*Sqrt[ -7 + 8*n]] && Mod[n - 7, 8] == 0, f[n], {}], {n, 1, 10000}]]
LinearRecurrence[{1, 1, -1}, {3, 12, 19}, 60] (* Harvey P. Dale, Oct 05 2017 *)
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PROG
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(PARI) Vec(x*(3 + 9*x + 4*x^2) / ((1 - x)^2 * (1 + x)) + O(x^100)) \\ Colin Barker, Nov 29 2016
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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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