OFFSET
0,4
REFERENCES
G. van der Geer, Hilbert Modular Surfaces, Springer-Verlag, 1988; p. 191, Cor. 2.2.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
G. van der Geer, Hilbert Modular Surfaces, in: Ergebnisse der Mathematik und ihrer Grenzgebiete. 3. Folge / A Series of Modern Surveys in Mathematics, Band 16, Springer-Verlag (1988).
Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1,1,-1,0,-1,1).
FORMULA
G.f.: (1+x^20)/((1-x)*(1-x^3)*(1-x^5)).
MATHEMATICA
CoefficientList[Series[(1 + x^20)/((1 - x)*(1 - x^3)*(1 - x^5)), {x, 0, 100}], x] (* Wesley Ivan Hurt, Mar 30 2017 *)
LinearRecurrence[{1, 0, 1, -1, 1, -1, 0, -1, 1}, {1, 1, 1, 2, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 17, 18, 21}, 68] (* G. C. Greubel, Dec 20 2017; more initial terms by Georg Fischer, Apr 08 2019 *)
PROG
(PARI) x='x+O('x^30); Vec((1+x^20)/((1-x)*(1-x^3)*(1-x^5))) \\ G. C. Greubel, Dec 20 2017
(Magma) I:=[1, 1, 1, 2, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 17, 18, 21];
[n le 21 select I[n] else Self(n-1) + Self(n-3) - Self(n-4) + Self(n-5) - Self(n-6) - Self(n-8) + Self(n-9): n in [1..80]]; // G. C. Greubel, Dec 20 2017; more initial terms by Georg Fischer, Apr 03 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Sep 05 2004
STATUS
approved