OFFSET
1,2
COMMENTS
When are both n+1 and 19*n+1 perfect squares? This gives the equation 19*x^2-18=y^2.
LINKS
Index entries for linear recurrences with constant coefficients, signature (0,0,340,0,0,-1).
FORMULA
a(n) = 340*a(n-3)+a(n-6), a(1)=1, a(2)=9, a(3)=131, a(4)=209, a(5)=3051, a(6)=44539.
G.f.: -x*(x-1)*(x^4+10*x^3+141*x^2+10*x+1) / (x^6-340*x^3+1). - Colin Barker, Sep 01 2013
EXAMPLE
a(7)=340*209-1=71059.
MATHEMATICA
LinearRecurrence[{0, 0, 340, 0, 0, -1}, {1, 9, 131, 209, 3051, 44539}, 50]
PROG
(PARI) Vec(-x*(x-1)*(x^4+10*x^3+141*x^2+10*x+1)/(x^6-340*x^3+1) + O(x^100)) \\ Colin Barker, Sep 01 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Sture Sjöstedt, Nov 17 2011
STATUS
approved