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).

7, 17, 117, 913, 1183, 1391, 13107, 51257, 151257, 381397, 577661, 4911789, 29116879, 112646989, 536920981, 1928258999, 11928258999, 25227472837, 46275452231, 212892173679, 370964057893, 1859199550327, 5593332415439

Offset

1,1

Links

Table of n, a(n) for n=1..23.

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, 7, 25 ]

Crossrefs

Cf. A003681, A062094 and A062095.

Sequence in context: A205989 A262474 A284416 * A165246 A266382 A118108

Adjacent sequences: A063381 A063382 A063383 * A063385 A063386 A063387

Keyword

base,nonn

Author

Robert G. Wilson v, Aug 09 2001

Status

approved