a(n) = floor((n + 1/2) * sqrt(2)).

Terms

a(0) =0a(1) =2a(2) =3a(3) =4a(4) =6a(5) =7a(6) =9a(7) =10a(8) =12a(9) =13a(10) =14a(11) =16a(12) =17a(13) =19a(14) =20a(15) =21a(16) =23a(17) =24a(18) =26a(19) =27a(20) =28a(21) =30a(22) =31a(23) =33a(24) =34a(25) =36a(26) =37a(27) =38a(28) =40a(29) =41