A062095 a(1) = 1, 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).

1, 11, 111, 337, 1337, 7191, 51141, 317047, 1317047, 2814687, 9312743, 25193697, 30981533, 51496017, 192326779, 1427134777, 4987286171, 6471777063, 61653104971, 259323776747, 737046253821, 7171027958513, 31727922601647

Offset

1,2

Links

Sean A. Irvine, Table of n, a(n) for n = 1..250

Example

a(3) = 111 hence a(4) = 337, as 3*37 = 111 and 3 < 37.

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, 1, 25]

Crossrefs

Cf. A062094, A003681.

Sequence in context: A092819 A336523 A209233 * A055657 A049121 A143573

Adjacent sequences: A062092 A062093 A062094 * A062096 A062097 A062098

Keyword

nonn,easy,base

Author

Amarnath Murthy, Jun 16 2001

Extensions

More terms from Robert G. Wilson v, Aug 08 2001

Status

approved