Repunit powers.

Terms

a(0) =1a(1) =11a(2) =111a(3) =121a(4) =1111a(5) =1331a(6) =11111a(7) =12321a(8) =14641a(9) =111111a(10) =161051a(11) =1111111a(12) =1234321a(13) =1367631a(14) =1771561a(15) =11111111a(16) =19487171a(17) =111111111a(18) =123454321a(19) =151807041a(20) =214358881a(21) =1111111111a(22) =1371330631a(23) =2357947691a(24) =11111111111