OFFSET
1,2
FORMULA
Empirical g.f.: x*(1 + x - x^4 - 4*x^5 - 6*x^6 - 23*x^10 - 29*x^11 + 69*x^12 - 14*x^13) / (1 - x - x^2). - Colin Barker, Nov 13 2016
EXAMPLE
a(4) = 5 because (1-x), (1-x)(1-x^2), and (1-x)(1-x^2)(1-x^3)(1-x^5) all have coefficients -1, 0, 1, but (1-x)(1-x^2)(1-x^3)(1-x^4) doesn't.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Shallit, Jul 05 2016
EXTENSIONS
a(19)-a(41) from Jon E. Schoenfield, Nov 12 2016
STATUS
approved