%F A128862 (?)

[N. J. A. Sloane]

> %F A128862 Define x(n) and y(n) by x(n) + y(n)*sqrt(3) = (3+sqrt(3))*(2+sqrt(3))^n; let s(n)  = (y(n)+1)/2; then a(n) = (1/2)*(2+3*(s(n)^2-s(n))).

A simpler formula:

%Y A128862 Equals (3*A001570(n) + 1)/4.


ralf