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A243843 a(n) is the smallest semiprime that belongs to a cycle of length n under repeated iteration of the map (k -> concatenation of prime divisors of k) until a non-semiprime is reached. 0

%I

%S 6,38,34,15,265,161,1126,4891,1253,250231,100462,49869178,234139657,

%T 68279314

%N a(n) is the smallest semiprime that belongs to a cycle of length n under repeated iteration of the map (k -> concatenation of prime divisors of k) until a non-semiprime is reached.

%H Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_640.htm">Puzzle 640</a>

%K nonn,base,hard,more

%O 1,1

%A _Arkadiusz Wesolowski_, Jun 13 2014

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Last modified July 3 18:04 EDT 2022. Contains 355055 sequences. (Running on oeis4.)