Repunit pseudoprimes: composite numbers k such that (10^k - 1)/9 == 1 (mod k).

Terms

a(0) =10a(1) =55a(2) =91a(3) =259a(4) =370a(5) =385a(6) =451a(7) =481a(8) =505a(9) =703a(10) =715a(11) =1045a(12) =1105a(13) =1729a(14) =2035a(15) =2465a(16) =2821a(17) =2981a(18) =3367a(19) =4141a(20) =4187a(21) =5005a(22) =5461a(23) =6533a(24) =6541a(25) =6565a(26) =6601a(27) =7471a(28) =7777a(29) =8149