OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..2000
FORMULA
EXAMPLE
a(0)=390 because 30 follows the prime 29 and has four prime factors 2, 3, 5 and 13.
MATHEMATICA
Select[Prime[Range[400]]+1, PrimeNu[#]==4&] (* Harvey P. Dale, Aug 15 2021 *)
PROG
(PARI) isok(n) = (omega(n)==4) && isprime(n-1); \\ Michel Marcus, Jun 08 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Enoch Haga, Dec 16 2007
EXTENSIONS
Edited by R. J. Mathar, Feb 20 2008
STATUS
approved