A357023 Semiprimes k such that k is congruent to 5 modulo k's index in the sequence of semiprimes.

4, 185, 206, 209, 27681, 3066905, 3067135, 3067795, 3067985, 348933197, 348933239, 348933251, 348933257, 348933269, 44690978141, 44690978162, 44690978519, 44690978561, 44690978617, 44690978869, 44690978981, 44690979457, 44690979527, 6553736049293

Offset

1,1

Comments

a(32) > 8040423200947.

Links

Lucas A. Brown, Table of n, a(n) for n = 1..31

Lucas A. Brown, semiprimemods.py.

Formula

a(n) = A001358(A106130(n)).

Example

The 1st semiprime is 4, which is congruent to 5 (mod 1), so 4 is in the sequence.
The 2nd semiprime is 6, which is not congruent to 5 (mod 6), so 6 is not in the sequence.
The 60th semiprime is 185, which is congruent to 5 (mod 60), so 185 is in the sequence.

Crossrefs

Cf. A001358, A106130.

Sequence in context: A146549 A156905 A202631 * A102194 A102191 A358809

Adjacent sequences: A357020 A357021 A357022 * A357024 A357025 A357026

Keyword

nonn,hard

Author

Lucas A. Brown, Oct 14 2022

Status

approved