A357781 Semiprimes k such that k is congruent to 1 modulo k's index in the sequence of semiprimes.

4, 82, 85, 106, 121, 133, 142, 166, 169, 217, 3067001, 3067006, 3067286, 3067411, 3067651, 3067691, 3067721, 3067751, 3067771, 3067781, 3067801, 3068071, 348933121, 348933127, 348933199, 348933223, 348933241, 348933259, 348933271, 348933427, 44690978221, 44690978543, 44690978669

Offset

1,1

Comments

a(45) > 8040423200947.

Links

Lucas A. Brown, Table of n, a(n) for n = 1..44

Lucas A. Brown, semiprimemods.py

Formula

a(n) = A001358(A106126(n)).

Example

The 1st semiprime is 4, which is congruent to 1 (mod 1), so 4 is in the sequence.
The 4th semiprime is 10, which is congruent to 2 (mod 4), so 10 is not in the sequence.
The 27th semiprime is 82, which is congruent to 1 (mod 27), so 82 is in the sequence.

Crossrefs

Cf. A001358, A106126.

Sequence in context: A090599 A133396 A233001 * A318868 A289224 A158981

Adjacent sequences: A357778 A357779 A357780 * A357782 A357783 A357784

Keyword

nonn,hard

Author

Lucas A. Brown, Oct 13 2022

Status

approved