A168630 Numbers n such that n, n+1, and the sum of those two numbers each have 4 or more distinct prime factors.

46189, 50634, 69597, 76797, 90117, 97954, 108205, 115804, 127347, 138957, 144627, 159340, 164020, 166022, 166497, 166705, 167205, 167485, 173194, 174454, 181670, 186294, 190014, 193154, 198789, 211029, 212134, 214225, 217217, 221815, 222547, 224146

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

FactorInteger[46189]=11*13*17*19, FactorInteger[46190]=2*5*31*149, FactorInteger[46189+46190]=3*7*53*83,..

Maple

g:= proc(n) option remember; nops(numtheory:-factorset(n))>=4 end proc:
filter:= n -> g(n) and g(n+1) and g(2*n+1):
select(filter, [$1..300000]); # Robert Israel, May 09 2018

Mathematica

f[n_]:=Length[FactorInteger[n]]; lst={}; Do[If[f[n]>=4&&f[n+1]>=4&&f[n+n+1]>=4, AppendTo[lst, n]], {n, 9!}]; lst
Select[Range[225000], Min[Thread[PrimeNu[{#, #+1, 2#+1}]]]>3&](* Harvey P. Dale, Nov 11 2017 *)

Crossrefs

Cf. A140077, A140078, A168626, A168628, A168629

Sequence in context: A061405 A061529 A115939 * A361035 A190882 A251278

Adjacent sequences: A168627 A168628 A168629 * A168631 A168632 A168633

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Dec 01 2009

Extensions

Definition modified and terms extended by Harvey P. Dale, Nov 11 2017

Status

approved