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%I #15 Apr 10 2021 10:32:45
%S 8,12,102,1001,10002,100006,1000002,10000005,100000006,1000000003,
%T 10000000001,100000000006,1000000000001,10000000000001,
%U 100000000000018,1000000000000002,10000000000000006,100000000000000007,1000000000000000001,10000000000000000007
%N Smallest n-digit number that is divisible by exactly 3 primes (counted with multiplicity).
%C This is to 3 as smallest n-digit semiprime A098449 is to 2, and as smallest n-digit prime A003617 is to 1. Smallest n-digit triprime. Smallest n-digit 3-almost prime.
%e a(1) = 8 because 8=2^3 is the smallest (only) 1-digit number divisible by exactly 3 primes (counted with multiplicity).
%e 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).
%e a(3) = 102 because 102 = 2 * 3 * 17 is the smallest 3-digit numbers divisible by exactly 3 primes (counted with multiplicity).
%o (PARI) A180922(n)=for(n=10^(n-1),10^n-1,bigomega(n)==3&return(n)) \\ _M. F. Hasler_, Jan 23 2011
%o (Python)
%o from sympy import factorint
%o def triprimes(n): f = factorint(n); return sum(f[p] for p in f) == 3
%o def a(n):
%o an = max(1, 10**(n-1))
%o while not triprimes(an): an += 1
%o return an
%o print([a(n) for n in range(1, 21)]) # _Michael S. Branicky_, Apr 10 2021
%Y Cf. A003617, A014612, A098449.
%K nonn,base,easy
%O 1,1
%A _Jonathan Vos Post_, Jan 23 2011
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