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 A108970 Concatenation of triangular number k and its 10's complement is prime. 0
 1, 3, 21, 91, 561, 861, 903, 1953, 3003, 3741, 5151, 13203, 16653, 17391, 22791, 25651, 29161, 29403, 44253, 45753, 56953, 57291, 64261, 87153, 88831, 97903, 102831, 118341, 128271, 157641, 178503, 179101, 203841, 208981, 216811, 229503 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS tri(2^361+201) generates a prime with 436 digits. LINKS EXAMPLE a(5)=561 because 1000-561 = 439 and 561439 is prime. CROSSREFS Sequence in context: A083231 A129755 A059826 * A069017 A264246 A144883 Adjacent sequences: A108967 A108968 A108969 * A108971 A108972 A108973 KEYWORD easy,nonn,base AUTHOR Jason Earls, Jul 27 2005 STATUS approved

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Last modified December 1 23:44 EST 2022. Contains 358485 sequences. (Running on oeis4.)