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).

9, 33, 311, 1311, 2357, 12357, 91373, 191373, 273701, 594639, 966071, 3792549, 7714919, 18474177, 36158059, 217166627, 415296747, 1269327263, 8581147923, 85531003291, 307572780863, 417501775143, 594709702027, 1334471501519

Offset

1,1

Links

Table of n, a(n) for n=1..24.

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, 9, 25 ]

Crossrefs

Cf. A003681, A062094 and A062095.

Sequence in context: A013488 A186762 A343843 * A183939 A145952 A172498

Adjacent sequences: A063420 A063421 A063422 * A063424 A063425 A063426

Keyword

base,nonn

Author

Robert G. Wilson v, Aug 09 2001

Status

approved