A134190 a(1)=1. a(n) = n*a(n-1) if n*a(n-1) has a fewer number of divisors than n+a(n-1) does. a(n) = n+a(n-1) if n*a(n-1) has a greater or equal number of divisors than n+a(n-1) does.

1, 3, 9, 13, 65, 71, 497, 505, 514, 524, 535, 547, 7111, 7125, 106875, 106891, 1817147, 1817165, 34526135, 34526155, 34526176, 34526198, 34526221, 34526245, 34526270, 897683020, 897683047, 897683075, 897683104, 897683134, 897683165, 897683197

Offset

1,2

Links

Table of n, a(n) for n=1..32.

Example

a(6)+7 = 71 + 7 = 78. a(6)*7 = 71 * 7 = 497. 78 has 8 divisors. 497 has 4 divisors. Since 497 has fewer divisors than 78, a(7) is therefore 497.

Mathematica

a = {1}; For[n=2, n < 40, n++, If[Length[Divisors[n*a[[ -1]]]] < Length[Divisors[n+ a[[ -1]]]], AppendTo[a, n*a[[ -1]]], AppendTo[a, n + a[[ -1]]]]]; a (* Stefan Steinerberger, Oct 26 2007 *)

Crossrefs

Cf. A134189.

Sequence in context: A018292 A089147 A094043 * A047905 A134904 A358271

Adjacent sequences: A134187 A134188 A134189 * A134191 A134192 A134193

Keyword

nonn

Author

Leroy Quet, Oct 12 2007

Extensions

More terms from Stefan Steinerberger, Oct 26 2007

Status

approved