Powers of sqrt(19) rounded down.

Terms

a(0) =1a(1) =4a(2) =19a(3) =82a(4) =361a(5) =1573a(6) =6859a(7) =29897a(8) =130321a(9) =568056a(10) =2476099a(11) =10793065a(12) =47045881a(13) =205068240a(14) =893871739a(15) =3896296578a(16) =16983563041a(17) =74029634996a(18) =322687697779