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%I #3 Dec 15 2017 17:36:51
%S 1,3,21,91,561,861,903,1953,3003,3741,5151,13203,16653,17391,22791,
%T 25651,29161,29403,44253,45753,56953,57291,64261,87153,88831,97903,
%U 102831,118341,128271,157641,178503,179101,203841,208981,216811,229503
%N Concatenation of triangular number k and its 10's complement is prime.
%C tri(2^361+201) generates a prime with 436 digits.
%e a(5)=561 because 1000-561 = 439 and 561439 is prime.
%K easy,nonn,base
%O 1,2
%A _Jason Earls_, Jul 27 2005
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