a(n) is the smallest k > 1 such that n^k starts and ends with n, or -1 if there is no such k.

Terms

a(0) =2a(1) =21a(2) =41a(3) =11a(4) =24a(5) =10a(6) =33a(7) =73a(8) =153a(9) =-1a(10) =171a(11) =241a(12) =361a(13) =-1a(14) =-1a(15) =6a(16) =461a(17) =-1a(18) =471a(19) =-1a(20) =12086a(21) =-1a(22) =1281a(23) =51a(24) =94a(25) =-1a(26) =1181a(27) =701a(28) =1091a(29) =-1