OFFSET
1,1
COMMENTS
EXAMPLE
a(1) = 8 because 8=2^3 is the smallest (only) 1-digit number divisible by exactly 3 primes (counted with multiplicity).
a(2) = 12 because 12 = 2^2 * 3 is the smallest of the (21) 2-digit numbers divisible by exactly 3 primes (counted with multiplicity).
a(3) = 102 because 102 = 2 * 3 * 17 is the smallest 3-digit numbers divisible by exactly 3 primes (counted with multiplicity).
PROG
(PARI) A180922(n)=for(n=10^(n-1), 10^n-1, bigomega(n)==3&return(n)) \\ M. F. Hasler, Jan 23 2011
(Python)
from sympy import factorint
def triprimes(n): f = factorint(n); return sum(f[p] for p in f) == 3
def a(n):
an = max(1, 10**(n-1))
while not triprimes(an): an += 1
return an
print([a(n) for n in range(1, 21)]) # Michael S. Branicky, Apr 10 2021
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, Jan 23 2011
STATUS
approved