Sum_{i for which n - i*(i-1)/2 >= 0} binomial (n - i*(i-1)/2, i).

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =8a(5) =12a(6) =18a(7) =27a(8) =40a(9) =58a(10) =83a(11) =118a(12) =167a(13) =235a(14) =328a(15) =454a(16) =624a(17) =853a(18) =1161a(19) =1574a(20) =2125a(21) =2856a(22) =3821a(23) =5090a(24) =6754a(25) =8931a(26) =11773a(27) =15474a(28) =20280a(29) =26502