Concatenation of triangular number k and its 10's complement is prime.

Terms

a(0) =1a(1) =3a(2) =21a(3) =91a(4) =561a(5) =861a(6) =903a(7) =1953a(8) =3003a(9) =3741a(10) =5151a(11) =13203a(12) =16653a(13) =17391a(14) =22791a(15) =25651a(16) =29161a(17) =29403a(18) =44253a(19) =45753a(20) =56953a(21) =57291a(22) =64261a(23) =87153a(24) =88831a(25) =97903a(26) =102831a(27) =118341a(28) =128271a(29) =157641