OFFSET
1,2
COMMENTS
When are both n+1 and 15*n+1 perfect squares? This problem gives the equation 15*x^2-14=y^2.
Essentially the same as A103201. - R. J. Mathar, Nov 11 2011
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
Index entries for linear recurrences with constant coefficients, signature (0,8,0,-1).
FORMULA
a(n+4) = 8*a(n+2) - a(n) with a(1)=1, a(2)=11, a(3)=19, a(4)=89.
G.f.: x*(1+x)*(1+10*x+x^2)/(1-8*x^2+x^4). - Bruno Berselli, Nov 08 2011
MATHEMATICA
LinearRecurrence[{0, 8, 0, -1}, {1, 11, 19, 89}, 50]
PROG
(Magma) m:=29; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(x*(1+x)*(1+10*x+x^2)/(1-8*x^2+x^4))); // Bruno Berselli, Nov 08 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Sture Sjöstedt, Nov 08 2011
STATUS
approved