a(1)=1; for n > 1, a(n) = n - a(n-floor(sqrt(n))).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =3a(5) =3a(6) =4a(7) =5a(8) =6a(9) =6a(10) =6a(11) =6a(12) =7a(13) =8a(14) =9a(15) =10a(16) =10a(17) =10a(18) =10a(19) =10a(20) =11a(21) =12a(22) =13a(23) =14a(24) =15a(25) =15a(26) =15a(27) =15a(28) =15a(29) =15