Search: id:A120716
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%I A120716
%S A120716 1,2,3,2,5,23,7
%N A120716 a(1)=1, a(p)=p if p is a prime. Otherwise, start with n and iterate the 
               map (k -> concatenation of proper divisors of k) until we reach a 
               prime q; then a(n) = q. If we never reach a prime, a(n) = -1.
%H A120716 N. J. A. Sloane et al., <a href="a120716.txt">Notes on the attempt to 
               find a(8)</a>
%e A120716 4 -> 2, prime, so a(4) = 2.
%e A120716 6 -> 2,3 -> 23, prime, so a(6) = 23.
%e A120716 8 -> 2.4 -> 24 -> 2.3.4.6.8.12 -> 2346812 -> 2.4.13.26.52.45131.90262.180524.586703.1173406 
               -> 2413265245131902621805245867031173406 -> ? (see link for the continuation)
%e A120716 9 -> 3, prime, so a(9) = 3.
%e A120716 21 -> 3,7 -> 37, prime, so a(21) = 37.
%Y A120716 Cf. A120712, A120713, A037274, A130139-A130142. A130139 is a bisection.
%Y A120716 Sequence in context: A010242 A086507 A133568 this_sequence A084318 A084317 
               A037279
%Y A120716 Adjacent sequences: A120713 A120714 A120715 this_sequence A120717 A120718 
               A120719
%K A120716 nonn,base,more,hard
%O A120716 1,2
%A A120716 N. J. A. Sloane (njas(AT)research.att.com), Jul 19 2007
%E A120716 a(8) is currently unknown.

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