A168626 Numbers n such that n and n+-1 have 3 or more distinct prime factors.

645, 741, 805, 987, 1035, 1065, 1105, 1221, 1275, 1309, 1310, 1463, 1495, 1581, 1749, 1885, 1886, 1925, 1989, 2014, 2015, 2109, 2135, 2211, 2255, 2261, 2289, 2295, 2331, 2355, 2365, 2379, 2409, 2465, 2485, 2541, 2584, 2585, 2665, 2666, 2667, 2679, 2685

Offset

1,1

Links

Table of n, a(n) for n=1..43.

Mathematica

f[n_]:=Length[FactorInteger[n]]; lst={}; Do[If[f[n]>=3&&f[n-1]>=3&&f[n+1]>=3, AppendTo[lst, n]], {n, 7!}]; lst
Mean/@SequencePosition[Table[If[PrimeNu[n]>2, 1, 0], {n, 2700}], {1, 1, 1}] (* The program uses the SequencePosition function from Mathematica version 10 *) (* Harvey P. Dale, Jun 05 2016 *)

Crossrefs

Cf. A140077

Sequence in context: A364308 A260838 A304607 * A216023 A100873 A227136

Adjacent sequences: A168623 A168624 A168625 * A168627 A168628 A168629

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Dec 01 2009

Extensions

Definition clarified by Harvey P. Dale, Jun 05 2016

Status

approved