OFFSET
1,3
COMMENTS
Also nonnegative integers primitively represented by x^2 - y^2. - Ray Chandler, Aug 23 2014
LINKS
Ray Chandler, Table of n, a(n) for n = 1..10000
N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)
Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,1,-1).
FORMULA
G.f.: x^2*(x^2 + 1)*(1 + x)^2/((x^4 + x^3 + x^2 + x + 1)*(x - 1)^2). - R. J. Mathar, Oct 07 2011
From Wesley Ivan Hurt, Dec 28 2016: (Start)
a(n) = a(n-1) + a(n-5) - a(n-6) for n > 6.
a(n) = (40*n - 40 - 2*(n mod 5) - 2*((n+1) mod 5) - 2*((n+2) mod 5) + 3*((n+3) mod 5) + 3*((n+4) mod 5))/25. (End)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved