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A168630 Numbers n such that n, n+1, and the sum of those two numbers each have 4 or more distinct prime factors. 1
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 (list; graph; refs; listen; history; text; internal format)
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 * A190882 A251278 A202897

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

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Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)