OFFSET
1,2
COMMENTS
Also values x of Pythagorean triples (x, x+601, y).
Corresponding values y of solutions (x, y) are in A160098.
lim_{n -> infinity} a(n)/a(n-3) = 3+2*sqrt(2).
lim_{n -> infinity} a(n)/a(n-1) = (843+418*sqrt(2))/601 for n mod 3 = {1, 2}.
lim_{n -> infinity} a(n)/a(n-1) = (361299+5950*sqrt(2))/601^2 for n mod 3 = 0.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,0,6,-6,0,-1,1).
FORMULA
a(n) = 6*a(n-3) - a(n-6) + 1202 for n > 6; a(1)=0, a(2)=539, a(3)=560, a(4)=1803, a(5)=4740, a(6)=4859.
G.f.: x*(539 +21*x +1243*x^2 -297*x^3 -7*x^4 -297*x^5)/((1-x)*(1 -6*x^3 +x^6)).
a(3*k+1) = 601*A001652(k) for k >= 0.
MATHEMATICA
LinearRecurrence[{1, 0, 6, -6, 0, -1, 1}, {0, 539, 560, 1803, 4740, 4859, 12020}, 50] (* G. C. Greubel, Apr 22 2018 *)
PROG
(PARI) {forstep(n=0, 10000000, [3, 1], if(issquare(2*n^2+1202*n+361201), print1(n, ", ")))}
(PARI) x='x+O('x^30); concat([0], Vec(x*(539 +21*x +1243*x^2 -297*x^3 -7*x^4 -297*x^5)/((1-x)*(1 -6*x^3 +x^6)))) \\ G. C. Greubel, Apr 22 2018
(Magma) I:=[0, 539, 560, 1803, 4740, 4859, 12020]; [n le 7 select I[n] else Self(n-1) + 6*Self(n-3) - 6*Self(n-4) -Self(n-6) + Self(n-7): n in [1..30]]; // G. C. Greubel, Apr 22 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Mohamed Bouhamida, Jun 03 2007
EXTENSIONS
Edited and one term added by Klaus Brockhaus, May 18 2009
STATUS
approved