A321504 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

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

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 *)

PROG

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

CROSSREFS

Cf. A140078, A321494.

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

Sequence in context: A253939 A116248 A140078 * A318896 A328786 A295004

Adjacent sequences: A321501 A321502 A321503 * A321505 A321506 A321507

KEYWORD

nonn

AUTHOR

M. F. Hasler, Nov 12 2018

STATUS

approved