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A063269 a(1) = 3, 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 A063269 #2 Mar 30 2012 17:30:32
%S A063269 3,13,113,1113,2153,12153,34051,172003,1311313,3473779,5365543,
%T A063269 16913173,34014973,229148537,479347809,1807726517,11807726517,
%U A063269 20529575173,69833293981,179443389167,230839777353,376946592451
%N A063269 a(1) = 3, 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 A063269 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, 3, 24 ]
%Y A063269 Cf. A003681, A062094 and A062095.
%K A063269 base,nonn
%O A063269 1,1
%A A063269 _Robert G. Wilson v_, Aug 08 2001