G.f.: Sum_{n>=0} (1+x + x^n)^n * x^n.

Terms

a(0) =1a(1) =1a(2) =3a(3) =3a(4) =7a(5) =10a(6) =17a(7) =27a(8) =41a(9) =70a(10) =109a(11) =168a(12) =276a(13) =439a(14) =688a(15) =1099a(16) =1774a(17) =2820a(18) =4488a(19) =7219a(20) =11596a(21) =18574a(22) =29844a(23) =48040a(24) =77302a(25) =124515a(26) =200756a(27) =323695a(28) =522168a(29) =843020