A168628 Numbers n such that n and n+-1 have 4 distinct prime factors.

37961, 44485, 45695, 50141, 51429, 55131, 55385, 61335, 63365, 64295, 67165, 68265, 68475, 70005, 70091, 71709, 72709, 76153, 80445, 81549, 81719, 82041, 84435, 85491, 86241, 90364, 95381, 97383, 98021, 99085, 99385, 99429, 99789, 100165, 100491, 100595

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Dec 01 2009

Keywords

• nonn

Crossrefs

Subsequence of A140078.

Cf. A140077, A168626

Programs

Mathematica

f[n_]:=Length[FactorInteger[n]]; lst={};Do[If[f[n]>=4&&f[n-1]>=4&&f[n+1]>=4,AppendTo[lst,n]],{n,9!}];lst
SequencePosition[PrimeNu[Range[110000]],{4,4,4}][[All,1]]+1 (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 27 2018 *)

PARI

is(n)=omega(n)==4 && omega(n+1)==4 && omega(n-1)==4 \\ Charles R Greathouse IV, Jan 25 2025

Extensions

Corrected and extended by Harvey P. Dale, Apr 27 2018