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A097922
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G.f.: (1-x^4)*(1-x^10)/((1-x)*(1-x^2)^2*(1-x^3)*(1-x^5)).
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2
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1, 1, 3, 4, 6, 9, 12, 16, 21, 26, 32, 39, 46, 54, 63, 72, 82, 93, 104, 116, 129, 142, 156, 171, 186, 202, 219, 236, 254, 273, 292, 312, 333, 354, 376, 399, 422, 446, 471, 496, 522, 549, 576, 604, 633, 662, 692, 723, 754, 786, 819, 852, 886, 921, 956, 992, 1029, 1066, 1104
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OFFSET
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0,3
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REFERENCES
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G. van der Geer, Hilbert Modular Surfaces, Springer-Verlag, 1988; p. 188.
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LINKS
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FORMULA
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a(n) = 2 + ceiling((n^2 - n)/3) for n >= 2. - Robert Israel, May 20 2014
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MATHEMATICA
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CoefficientList[Series[(1-x^4)*(1-x^10)/((1-x)*(1-x^2)^2*(1-x^3)*(1-x^5)), {x, 0, 50}], x] (* or *) Join[{1, 1}, LinearRecurrence[{2, -1, 1, -2, 1}, {3, 4, 6, 9, 12}, 30]] (* or *) Join[{1, 1}, Table[2 + Ceiling[n*(n-1)/3], {n, 2, 30}]] (* G. C. Greubel, Dec 20 2017 *)
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PROG
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(PARI) x='x+O('x^30); Vec((1-x^4)*(1-x^10)/((1-x)*(1-x^2)^2*(1-x^3)*(1-x^5))) \\ G. C. Greubel, Dec 20 2017
(PARI) for(n=0, 30, print1(if(n==0, 1, if(n==1, 1, 2 + ceil(n*(n-1)/3))), ", ")) \\ G. C. Greubel, Dec 20 2017
(Magma) [1, 1] cat [2 + Ceiling(n*(n-1)/3): n in [2..30]]; // G. C. Greubel, Dec 20 2017
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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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