OFFSET
0,1
LINKS
Paolo Xausa, Table of n, a(n) for n = 0..500
J.-P. Ehrmann et al., Problem POLYA002, Integer pairs (x,y) for which (x^2+y^2)/(1+pxy) is an integer.
Index entries for linear recurrences with constant coefficients, signature (21,-21,1).
FORMULA
a(n) = 2t(m)a(n-1)-a(n-2)-1, a(0) = m, a(1) = m^3+m^2-1 with m = 4.
G.f.: (5x-4)/((1-20x+x^2)(x-1)).
MAPLE
g := (5*x-4)/(1-20*x+x^2)/(x-1): s := series(g, x, 40): for i from 0 to 30 do printf(`%d, `, coeff(s, x, i)) od: # James A. Sellers, Feb 11 2002
MATHEMATICA
LinearRecurrence[{21, -21, 1}, {4, 79, 1575}, 25] (* Paolo Xausa, Jan 08 2024 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Floor van Lamoen, Nov 29 2001
EXTENSIONS
More terms from James A. Sellers, Feb 11 2002
STATUS
approved