FW: A101368

[Floor en Lyanne van Lamoen]

I think that the following direct formula follows from this:

a(n) = (4/3-2/7*sqrt(21))*((5+sqrt(21))/2)^n
     +(4/3+2/7*sqrt(21))*((5-sqrt(21))/2)^n + 1/3

Floor.