OFFSET
1,2
COMMENTS
Also values x of Pythagorean triples (x, x+73, y).
Corresponding values y of solutions (x, y) are in A160041.
lim_{n -> infinity} a(n)/a(n-3) = 3+2*sqrt(2).
lim_{n -> infinity} a(n)/a(n-1) = (89+36*sqrt(2))/73 for n mod 3 = {1, 2}.
lim_{n -> infinity} a(n)/a(n-1) = (5907+1802*sqrt(2))/73^2 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) +146 for n > 6; a(1)=0, a(2)=44, a(3)=95, a(4)=219, a(5)=455, a(6)=744.
G.f.: x*(44+51*x+124*x^2-28*x^3-17*x^4-28*x^5)/((1-x)*(1-6*x^3+x^6)).
a(3*k+1) = 73*A001652(k) for k >= 0.
MATHEMATICA
Select[Range[0, 100000], IntegerQ[Sqrt[#^2+(#+73)^2]]&] (* or *) LinearRecurrence[{1, 0, 6, -6, 0, -1, 1}, {0, 44, 95, 219, 455, 744, 1460}, 70] (* Vladimir Joseph Stephan Orlovsky, Feb 02 2012 *)
PROG
(PARI) {forstep(n=0, 100000000, [3 , 1], if(issquare(2*n^2+146*n+5329), print1(n, ", ")))}
(Magma) m:=25; R<x>:=PowerSeriesRing(Integers(), m); [0] cat Coefficients(R!(x*(44+51*x+124*x^2-28*x^3-17*x^4-28*x^5)/((1-x)*(1-6*x^3+x^6)))); // G. C. Greubel, May 07 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Mohamed Bouhamida, May 26 2007
EXTENSIONS
Edited and two terms added by Klaus Brockhaus, May 04 2009
STATUS
approved