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A063384 a(1) = 7, 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 A063384 #3 Mar 30 2012 17:30:32
%S A063384 7,17,117,913,1183,1391,13107,51257,151257,381397,577661,4911789,
%T A063384 29116879,112646989,536920981,1928258999,11928258999,25227472837,
%U A063384 46275452231,212892173679,370964057893,1859199550327,5593332415439
%N A063384 a(1) = 7, 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 A063384 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, 7, 25 ]
%Y A063384 Cf. A003681, A062094 and A062095.
%K A063384 base,nonn
%O A063384 1,1
%A A063384 _Robert G. Wilson v_, Aug 09 2001