OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1660
FORMULA
EXAMPLE
G.f. = 1 - 3*x - x^2 - 2*x^3 - 5*x^4 - 14*x^5 - 42*x^6 - 132*x^7 - 429*x^8 + ...
MATHEMATICA
CoefficientList[Series[(1 +Sqrt[1-4*x])/2 -2*x, {x, 0, 50}], x] (* G. C. Greubel, Aug 04 2018 *)
PROG
(PARI) {a(n) = if( n<2, (n==0) - 3*(n==1), - binomial(2*n - 2, n-1) / n)};
(PARI) {a(n) = if( n<0, 0, polcoeff( (1 + sqrt(1 - 4*x + x * O(x^n))) / 2 - 2*x, n))};
(Magma) m:=50; R<x>:=PowerSeriesRing(Rationals(), m); Coefficients(R!((1 +Sqrt(1-4*x))/2 -2*x)); // G. C. Greubel, Aug 04 2018
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Nov 14 2014
STATUS
approved