a(n) = n for n <= 2; for n > 2, a(n) = 2a(n-1) - a(n - floor(1/2 + sqrt(2(n-1)))).

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =6a(6) =9a(7) =14a(8) =24a(9) =42a(10) =75a(11) =136a(12) =258a(13) =492a(14) =942a(15) =1809a(16) =3482a(17) =6828a(18) =13398a(19) =26304a(20) =51666a(21) =101523a(22) =199564a(23) =395646a(24) =784464a(25) =1555530a(26) =3084756a(27) =6117846a(28) =12134169a(29) =24068774