OFFSET
1,2
COMMENTS
Diagonal sums of triangle A080245
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..300
FORMULA
G.f.: x*(-1-x+2*x^2+sqrt(1+6*x+x^2))/(2*x*(1+x+x^2-x^3)). - C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 19 2004
Conjecture: (n+1)*a(n) +(7*n-2)*a(n-1) +4*(2*n-1)*a(n-2) +6*(n-1)*a(n-3) +(-5*n+1)*a(n-4) +(-n+2)*a(n-5)=0. - R. J. Mathar, Nov 24 2012
MAPLE
seq(coeff(convert(series((-1-x+2*x^2+sqrt(1+6*x+x^2))/(2*x*(1+x+x^2-x^3)), x, 50), polynom), x, i), i=0..30); (C. Ronaldo)
MATHEMATICA
CoefficientList[Series[(-1 - x + 2 x^2 + Sqrt[1 + 6 x + x^2]) / (2 x (1 + x + x^2 - x^3)), {x, 0, 30}], x] (* Vincenzo Librandi, Aug 05 2013 *)
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Paul Barry, Feb 13 2003
EXTENSIONS
More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 19 2004
G.f. adapted to the offset by Vincenzo Librandi, Aug 05 2013
STATUS
approved