OFFSET
1,1
LINKS
Z. Franusic, On the Extension of the Diophantine Pair {1,3} in Z[surd d], J. Int. Seq. 13 (2010) # 10.9.6
Eric Weisstein's World of Mathematics, Diophantus Property.
Index entries for linear recurrences with constant coefficients, signature (15,-15,1).
FORMULA
G.f.: x(-4x^4+57x^3-14x^2-25x+2)/[(1-x)(1-14x+x^2)].
PROG
(PARI) a(n)=if(n>2, ([0, 1, 0; 0, 0, 1; 1, -15, 15]^(n-3)*[31; 449; 6271])[1, 1], 3*n-1) \\ Charles R Greathouse IV, Jun 02 2026
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved