A168629 Numbers n such that n,n+1 and sum of this two numbers have at least 3 distinct prime factors.

1105, 1130, 1462, 1644, 1742, 1767, 2014, 2222, 2232, 2260, 2337, 2365, 2397, 2464, 2541, 2667, 2684, 2697, 2702, 2755, 2821, 2914, 3074, 3115, 3195, 3289, 3332, 3477, 3484, 3514, 3552, 3619, 3657, 3685, 3782, 3783, 3842, 3965, 4014, 4088, 4122, 4147, 4277

Offset

1,1

Links

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

Example

1105 = 5*13*17, 1106 = 2*7*79, 1105 + 1106 = 2211 = 3*11*67.

Maple

q:= n-> andmap(x-> nops(numtheory[factorset](x))>2, [n, n+1, 2*n+1]):
select(q, [$1..4600])[];  # Alois P. Heinz, Jun 29 2021

Mathematica

f[n_]:=Length[FactorInteger[n]]; lst={}; Do[If[f[n]>=3&&f[n+1]>=3&&f[n+n+1]>=3, AppendTo[lst, n]], {n, 8!}]; lst

Crossrefs

Cf. A140077, A140078, A168626, A168628.

Sequence in context: A107519 A331641 A343084 * A175521 A214607 A321870

Adjacent sequences: A168626 A168627 A168628 * A168630 A168631 A168632

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Dec 01 2009

Status

approved