G.f.: Product_{n>=1} (1 + x^n + x^(n+1)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =7a(6) =10a(7) =15a(8) =21a(9) =28a(10) =38a(11) =52a(12) =70a(13) =92a(14) =119a(15) =154a(16) =200a(17) =258a(18) =329a(19) =416a(20) =523a(21) =655a(22) =819a(23) =1022a(24) =1269a(25) =1566a(26) =1924a(27) =2357a(28) =2879a(29) =3507