a(n) = |s(n) - n|, where s = A026250. Also a(n) = 2*t(n), where t = A026249.

Terms

a(0) =2a(1) =4a(2) =2a(3) =6a(4) =8a(5) =4a(6) =10a(7) =12a(8) =14a(9) =6a(10) =16a(11) =18a(12) =8a(13) =20a(14) =22a(15) =24a(16) =10a(17) =26a(18) =28a(19) =12a(20) =30a(21) =32a(22) =14a(23) =34a(24) =36a(25) =38a(26) =16a(27) =40a(28) =42a(29) =18