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A357807
Semiprimes k such that k is congruent to 3 modulo k's index in the sequence of semiprimes.
2
4, 9, 15, 111, 141, 237, 27663, 27667, 3066878, 3066893, 3067023, 3067033, 3067073, 3067193, 3067243, 3067273, 3067283, 3067543, 3067598, 3067613, 3067663, 3067798, 3067843, 3067853, 3067913, 3067933, 3067993, 348933171, 348933219, 348933297
OFFSET
1,1
COMMENTS
a(48) > 8040423200947.
LINKS
Lucas A. Brown, semiprimemods.py
FORMULA
a(n) = A001358(A106128(n)).
EXAMPLE
The 1st semiprime is 4, which is congruent to 3 (mod 1), so 4 is in the sequence.
The 2nd semiprime is 6, which is not congruent to 3 (mod 2), so 6 is not in the sequence.
The 3rd semiprime is 9, which is congruent to 3 (mod 3), so 9 is in the sequence.
The 4th semiprime is 10, which is not congruent to 3 (mod 4), so 10 is not in the sequence.
CROSSREFS
Sequence in context: A178379 A228553 A356928 * A337568 A070447 A106548
KEYWORD
nonn,hard
AUTHOR
Lucas A. Brown, Oct 13 2022
STATUS
approved