A321504 Numbers k such that k and k+1 each have at least 4 distinct prime factors.

7314, 8294, 8645, 9009, 10659, 11570, 11780, 11934, 13299, 13629, 13845, 14420, 15105, 15554, 16554, 16835, 17204, 17390, 17654, 17765, 18095, 18290, 18444, 18920, 19005, 19019, 19095, 19227, 20349, 20405, 20769, 21164, 21489, 21735, 22010, 22154, 22659, 23001, 23114, 23484, 23529, 23540, 23919, 24395

Offset: 1

Author

M. F. Hasler, Nov 12 2018

Keywords

• nonn

Comments

Equals A140078 up to a(123) but a({124, 214, 219, 276, 321, 415, ...}) = { 38570, 51414, 51765, 58695, 62985, 71070, ...} are not in A140078, see A321494.

Links

• M. F. Hasler, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A140078, A321494.

Cf. A321505, A321506 (variant for k=5 & k=6 prime factors).

Programs

Mathematica

SequencePosition[Table[If[PrimeNu[n]>3,1,0],{n,25000}],{1,1}][[All,1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 29 2019 *)

PARI

is(n)=omega(n)>=4&&omega(n+1)>=4