OFFSET
1,1
COMMENTS
Identical with A045933 from first-to 38th terms, but deviates later because A045933 includes start of chains with more than 2 prime-factors.
Contrary to longer chains(6,7,8,..) of omega=2 this sequence seems to be either infinite or very long. See A088963-A088985.
Primes counted without multiplicity. - Harvey P. Dale, Oct 20 2011
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..750 from Harvey P. Dale)
MATHEMATICA
Transpose[Select[Partition[Transpose[Select[Table[{n, PrimeNu[n]}, {n, 10000}], Last[#]==2&]][[1]], 5, 1], Last[#]-First[#]==4&]][[1]] (* Harvey P. Dale, Oct 20 2011 *)
PROG
(Python)
from sympy import primefactors
def ok(n):
return all(len(primefactors(n + i))==2 for i in range(5))
print([n for n in range(1, 8001) if ok(n)]) # Indranil Ghosh, Jul 17 2017
(PARI) lista(kmax) = {my(q = vector(5)); for(k = 6, kmax, q = concat(vecextract(q, "^1"), omega(k) == 2); if(vecmin(q) == 1, print1(k-4, ", "))); } \\ Amiram Eldar, Jul 11 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 30 2003
STATUS
approved