A063423 - OEIS

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 #2 Mar 30 2012 17:30:32

%S 9,33,311,1311,2357,12357,91373,191373,273701,594639,966071,3792549,

%T 7714919,18474177,36158059,217166627,415296747,1269327263,8581147923,

%U 85531003291,307572780863,417501775143,594709702027,1334471501519

%N 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 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 Cf. A003681, A062094 and A062095.

%K base,nonn

%O 1,1

%A _Robert G. Wilson v_, Aug 09 2001