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 A097922 G.f.: (1-x^4)*(1-x^10)/((1-x)*(1-x^2)^2*(1-x^3)*(1-x^5)). 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES G. van der Geer, Hilbert Modular Surfaces, Springer-Verlag, 1988; p. 188. LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (2,-1,1,-2,1). FORMULA a(n) = 2 + ceiling((n^2 - n)/3) for n >= 2. - Robert Israel, May 20 2014 MATHEMATICA 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 *) PROG (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 CROSSREFS Sequence in context: A283777 A202171 A182531 * A103109 A241639 A241655 Adjacent sequences:  A097919 A097920 A097921 * A097923 A097924 A097925 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Sep 05 2004 STATUS approved

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Last modified July 27 10:26 EDT 2021. Contains 346304 sequences. (Running on oeis4.)