OFFSET
1,2
LINKS
David A. Corneth, Table of n, a(n) for n = 1..349
FORMULA
From Michael S. Branicky, Sep 02 2022: (Start)
a(n) >= ceiling((A002110(n)-1)/3).
a(n) <= (c*A002110(n+1)/3-1)/3 for n > 1, and c = 1 or 2 chosen so the expression is an integer, with equality holding for c = 1 for n = 2, 3, 6, 7, ... . (End)
PROG
(Python)
from sympy import factorint, isprime
from itertools import count, islice
def f(n): return 1 if isprime(n) else len(factorint(n))
def agen():
n = 1
for k in count(0):
v = f(3*k+1)
while v >= n: yield k; n += 1
print(list(islice(agen(), 7))) # Michael S. Branicky, Sep 02 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Sep 02 2022
EXTENSIONS
a(8) from Michael S. Branicky, Sep 02 2022
a(9)-a(19) from Jon E. Schoenfield, Sep 02 2022
STATUS
approved