a(n) = round( 2*Gamma(3 + n/3) + 2^(n/3) ).

Terms

a(0) =5a(1) =7a(2) =10a(3) =14a(4) =21a(5) =33a(6) =52a(7) =85a(8) =144a(9) =248a(10) =438a(11) =791a(12) =1456a(13) =2731a(14) =5213a(15) =10112a(16) =19920a(17) =39819a(18) =80704a(19) =165749a(20) =344758a(21) =725888a(22) =1546398a(23) =3331879a(24) =7257856a(25) =15978098a(26) =35538283a(27) =79834112a(28) =181082105a(29) =414609369