OFFSET
0,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..5000
Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).
FORMULA
EXAMPLE
G.f. = 1 - x + 4*x^2 - 3*x^3 + 8*x^4 - 5*x^5 + 12*x^6 - 7*x^7 + 16*x^8 + ...
MATHEMATICA
a[ n_] := Which[ n < 1, Boole[n == 0], OddQ[n], -n, True, 2 n];
a[ n_] := SeriesCoefficient[ (1 - x + x^2) (1 + x^2) / (1 - x^2)^2, {x, 0, n}];
PROG
(PARI) {a(n) = if( n<1, n==0, n%2, -n, 2*n)};
(PARI) x='x+O('x^50); Vec((1-x+x^2)*(1+x^2)/(1-x^2)^2) \\ G. C. Greubel, Aug 04 2018
(Magma) m:=50; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1 - x+x^2)*(1+x^2)/(1-x^2)^2)); // G. C. Greubel, Aug 04 2018
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Michael Somos, Dec 27 2016
EXTENSIONS
Edited by M. F. Hasler, May 08 2018
STATUS
approved