%I A063423
%S A063423 9,33,311,1311,2357,12357,91373,191373,273701,594639,966071,3792549,
%T A063423 7714919,18474177,36158059,217166627,415296747,1269327263,8581147923,
%U A063423 85531003291,307572780863,417501775143,594709702027,1334471501519
%N A063423 a(1) = 9, a(n) = concatenation of two closest factors of a(n-1) whose 
               product equals a(n-1) or if a(n-1) is a prime then the concatenation 
               of 1 and a(n-1).
%t A063423 f[ n_Integer ] := (d = Divisors[ n ]; l = Length[ d ]; If[ EvenQ[ l ], 
               ToExpression[ ToString[ d[ [ l/2 ] ] ] <> ToString[ d[ [ l/2 + 1 
               ] ] ] ], ToExpression[ ToString[ d[ [ l/2 + .5 ] ] ] <> ToString[ 
               d[ [ l/2 + .5 ] ] ] ] ] ); NestList[ f, 9, 25 ]
%Y A063423 Cf. A003681, A062094 and A062095.
%Y A063423 Sequence in context: A146445 A046997 A013488 this_sequence A145952 A145925 
               A028568
%Y A063423 Adjacent sequences: A063420 A063421 A063422 this_sequence A063424 A063425 
               A063426
%K A063423 base,nonn
%O A063423 1,1
%A A063423 Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 09 2001