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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).

%I A063423 #2 Mar 30 2012 17:30:32
%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.
%K A063423 base,nonn
%O A063423 1,1
%A A063423 _Robert G. Wilson v_, Aug 09 2001