a(n) = least positive integer > a(n-1) and not a(i)^2 + a(j)^2 for 1<=i<=j<=n.

Terms

a(0) =2a(1) =3a(2) =4a(3) =5a(4) =6a(5) =7a(6) =9a(7) =10a(8) =11a(9) =12a(10) =14a(11) =15a(12) =16a(13) =17a(14) =19a(15) =21a(16) =22a(17) =23a(18) =24a(19) =26a(20) =27a(21) =28a(22) =30a(23) =31a(24) =33a(25) =35a(26) =36a(27) =37a(28) =38a(29) =39