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).

10, 25, 55, 511, 773, 1773, 9197, 17541, 91949, 143643, 347881, 3311051, 13311051, 35433757, 71499067, 72619847, 74179791, 82678973, 613313481, 1551395431, 1679289793, 4339053251, 6529966449, 9370214693, 71338602099, 222407320757

Offset: 1

Author

Robert G. Wilson v, Aug 09 2001

Keywords

• base
• nonn

Crossrefs

Cf. A003681, A062094 and A062095.

Programs

Mathematica

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 ]