a(n) = floor(11^n/3^n).

Terms

a(0) =1a(1) =3a(2) =13a(3) =49a(4) =180a(5) =662a(6) =2430a(7) =8910a(8) =32671a(9) =119796a(10) =439252a(11) =1610592a(12) =5905506a(13) =21653524a(14) =79396256a(15) =291119607a(16) =1067438559a(17) =3913941385a(18) =14351118413a(19) =52620767516a(20) =192942814227a(21) =707456985499