a(n) = floor(11^n/4^n).

Terms

a(0) =1a(1) =2a(2) =7a(3) =20a(4) =57a(5) =157a(6) =432a(7) =1189a(8) =3270a(9) =8994a(10) =24735a(11) =68023a(12) =187064a(13) =514428a(14) =1414678a(15) =3890365a(16) =10698505a(17) =29420889a(18) =80907445a(19) =222495474a(20) =611862556a(21) =1682622029a(22) =4627210579a(23) =12724829094a(24) =34993280009a(25) =96231520027a(26) =264636680074