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Composite numbers which divide the concatenation of their prime factors, with multiplicity, in ascending order.
10

%I #17 May 31 2024 22:04:19

%S 28749,21757820799,4373079629403

%N Composite numbers which divide the concatenation of their prime factors, with multiplicity, in ascending order.

%C a(2) found by _Jens Kruse Andersen_, who also cleverly derived 119 large terms of the sequence from the factorization of numbers of the form 10^k+1 (see Links).

%C 10^13 < a(4) <= 7810053011863508278028459 (the smallest of J. K. Andersen's large terms).

%H Michael S. Branicky, <a href="/A259047/a259047.txt">Python program for Andersen's algorithm extended to arbitrary base/ordering</a>.

%H Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_472.htm">Puzzle 472. What is the second solution?</a>, The Prime Puzzles & Problems Connection.

%H StackExchange, <a href="http://math.stackexchange.com/questions/1166424/numbers-divide-its-prime-factors-concatenation">New term in ascending order</a>.

%e 4373079629403 is equal to 3*367*2713*1464031 and it is a divisor of 336727131464031, hence it is in the sequence.

%Y Cf. A248915.

%K nonn,more,base,hard,bref

%O 1,1

%A _Giovanni Resta_, Jun 17 2015