A062094 a(1) = 2, 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).

2, 12, 34, 217, 731, 1743, 2183, 3759, 21179, 121179, 931303, 1931303, 11175573, 11379829, 17896361, 18419721, 96919009, 889910891, 1889910891, 2742368917, 25741106537, 110203233579, 679231622473, 1679231622473, 7921256096487

Offset

1,1

Links

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

Example

a(1) = 2 is a prime hence a(2) = 12; a(3) = 34, 3*4 = 12 and 3<4.

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, 2, 25]

Crossrefs

Cf. A003681, A062095.

Sequence in context: A055707 A055699 A244378 * A334838 A200543 A363453

Adjacent sequences: A062091 A062092 A062093 * A062095 A062096 A062097

Keyword

nonn,easy,base

Author

Amarnath Murthy, Jun 16 2001

Extensions

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

Status

approved