a(1)=1; thereafter a(n+1) = a(n)-n if a(n) >= n otherwise a(n+1) = a(n)+n.

Terms

a(0) =1a(1) =0a(2) =2a(3) =5a(4) =1a(5) =6a(6) =0a(7) =7a(8) =15a(9) =6a(10) =16a(11) =5a(12) =17a(13) =4a(14) =18a(15) =3a(16) =19a(17) =2a(18) =20a(19) =1a(20) =21a(21) =0a(22) =22a(23) =45a(24) =21a(25) =46a(26) =20a(27) =47a(28) =19a(29) =48