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).

3, 13, 113, 1113, 2153, 12153, 34051, 172003, 1311313, 3473779, 5365543, 16913173, 34014973, 229148537, 479347809, 1807726517, 11807726517, 20529575173, 69833293981, 179443389167, 230839777353, 376946592451

Offset

1,1

Links

Table of n, a(n) for n=1..22.

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, 3, 24 ]

Crossrefs

Cf. A003681, A062094 and A062095.

Sequence in context: A006860 A181083 A090537 * A105431 A360187 A053583

Adjacent sequences: A063266 A063267 A063268 * A063270 A063271 A063272

Keyword

base,nonn

Author

Robert G. Wilson v, Aug 08 2001

Status

approved