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A376800
3-brilliant numbers with distinct prime factors.
1
30, 42, 70, 105, 2431, 2717, 3289, 3553, 4147, 4199, 4301, 4433, 4807, 5083, 5291, 5423, 5681, 5797, 5863, 6061, 6149, 6409, 6479, 6721, 6851, 6919, 7163, 7337, 7429, 7579, 7657, 7667, 7733, 7843, 8041, 8177, 8437, 8569, 8671, 8723, 8789, 8987, 9061, 9139, 9269
OFFSET
1,1
LINKS
EXAMPLE
30 = 2*3*5 is a term.
2431 = 11*13*17 is a term.
PROG
(Python)
from sympy import factorint
def ok(n):
f = factorint(n)
return len(f) == sum(f.values()) == 3 and len(set([len(str(p)) for p in f])) == 1
print([k for k in range(9300) if ok(k)]) # Michael S. Branicky, Oct 05 2024
(Python)
from math import prod
from sympy import primerange
from itertools import count, combinations, islice
def bgen(d): # generator of terms that are products of d-digit primes
primes, out = list(primerange(10**(d-1), 10**d)), set()
for t in combinations(primes, 3): out.add(prod(t))
yield from sorted(out)
def agen(): # generator of terms
for d in count(1): yield from bgen(d)
print(list(islice(agen(), 45))) # Michael S. Branicky, Oct 05 2024
CROSSREFS
Intersection of A376703 and A007304.
Sequence in context: A367481 A219742 A348557 * A257832 A050776 A268697
KEYWORD
nonn,base,easy
AUTHOR
Paul Duckett, Oct 04 2024
EXTENSIONS
a(6) and beyond from Michael S. Branicky, Oct 05 2024
STATUS
approved