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%I #11 Oct 15 2019 12:04:53
%S 25,35,56,62,69,72,76,85,90,100,114,125,138,143,152,189,213,221,238,
%T 250,259,260,270,275,278,303,318,333,364,366,369,390,403,441,448,454,
%U 469,470,473,485,507,512,519,522,529,559,560,572,588,591,624,629,648
%N Numbers requiring 3 steps to reach a prime under the prime factor concatenation procedure.
%H Patrick De Geest, <a href="http://www.worldofnumbers.com/topic1.htm">Home Primes</a>
%e 69 = 3*23 -> 323 = 17*19 -> 1719 = 3*3*191 and 33191 is prime.
%Y Cf. A037271, A046411.
%K nonn,base
%O 1,1
%A _Patrick De Geest_, Jun 15 1998
%E Edited by _Charles R Greathouse IV_, Apr 28 2010
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