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

Author

Lucas A. Brown, Oct 14 2022

Keywords

• nonn
• hard

Comments

a(32) > 8040423200947.

Examples

			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.
		

Links

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

Crossrefs

Cf. A001358, A106130.

Formula

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