A357807 Semiprimes k such that k is congruent to 3 modulo k's index in the sequence of semiprimes.

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, Table of n, a(n) for n = 1..47

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

Cf. A001358, A106128.

Sequence in context: A178379 A228553 A356928 * A337568 A070447 A106548

Adjacent sequences: A357804 A357805 A357806 * A357808 A357809 A357810

Keyword

nonn,hard

Author

Lucas A. Brown, Oct 13 2022

Status

approved