Numbers k for which k^2 + (k')^2 is a square, where k' is the arithmetic derivative of k (A003415).

Terms

a(0) =0a(1) =1a(2) =12a(3) =15a(4) =35a(5) =81a(6) =143a(7) =323a(8) =400a(9) =441a(10) =899a(11) =1540a(12) =1763a(13) =2700a(14) =3599a(15) =4641a(16) =5183a(17) =5929a(18) =9375a(19) =10395a(20) =10403a(21) =11663a(22) =13585a(23) =18225a(24) =19043a(25) =21952a(26) =22499a(27) =30576a(28) =32399a(29) =35581