OFFSET
1,1
COMMENTS
Factorization in S_3 is not unique; for example, 220 = 4 * 55 = 10 * 22.
MATHEMATICA
nn = 100; Complement[Table[3 k + 1, {k, 1, nn}], Union[Flatten[ Table[Table[(3 k + 1) (3 j + 1), {k, 1, j}], {j, 1, nn}]]]]
PROG
(PARI) isok(m) = ((m % 3)==1) && (#select(x->((x%3)==1), divisors(m)) == 2); \\ Michel Marcus, Oct 06 2021
(Python)
nn = 300
s = [True]*((nn)//3 + 1)
for i in range(4, nn, 3):
if s[(i-1)//3]:
for t in range(4, (nn)//i, 3):
s[(i*t-1)//3] = False
print([3*i + 1 for i in range(1, (nn + 3)//3) if s[i]])
CROSSREFS
KEYWORD
nonn
AUTHOR
Gleb Ivanov, Oct 03 2021
STATUS
approved