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A063424 a(1) = 10, 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 A063424 #2 Mar 30 2012 17:30:32
%S A063424 10,25,55,511,773,1773,9197,17541,91949,143643,347881,3311051,
%T A063424 13311051,35433757,71499067,72619847,74179791,82678973,613313481,
%U A063424 1551395431,1679289793,4339053251,6529966449,9370214693,71338602099,222407320757
%N A063424 a(1) = 10, 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 A063424 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, 10, 25 ]
%Y A063424 Cf. A003681, A062094 and A062095.
%K A063424 base,nonn
%O A063424 1,1
%A A063424 _Robert G. Wilson v_, Aug 09 2001