Smallest prime obtained by appending one or more 3's to n, or -1 if no such prime exists.

Terms

a(0) =13a(1) =23a(2) =-1a(3) =43a(4) =53a(5) =-1a(6) =73a(7) =83a(8) =-1a(9) =103a(10) =113a(11) =-1a(13) =1433a(14) =-1a(15) =163a(16) =173a(17) =-1a(18) =193a(19) =20333a(20) =-1a(21) =223a(22) =233a(23) =-1a(24) =2533333333a(25) =263a(26) =-1a(27) =283a(28) =293a(29) =-1a(30) =313