A357808 Semiprimes k such that k is congruent to 4 modulo k's index in the sequence of semiprimes.

4, 6, 14, 115, 118, 178, 187, 214, 235, 3066899, 3067069, 3067079, 3067149, 3067429, 3067549, 3067594, 3067609, 3067669, 3067719, 3067999, 44690978147, 44690978217, 44690978245, 44690978623, 44690978903, 44690979022, 44690979442

Offset: 1

Author

Lucas A. Brown, Oct 13 2022

Keywords

• nonn
• hard
• more

Comments

a(28) > 8040423200947.

a(28) <= 1095927464608618, a(29) <= 1095927464608951 and a(38) <= 1095927464630173. - Martin Ehrenstein, Oct 28 2022

Examples

			The 1st semiprime is 4, which is congruent to 4 (modulo 1), so 4 is in the sequence.
The 2nd semiprime is 6, which is congruent to 4 (modulo 2), so 6 is in the sequence.
The 3rd semiprime is 9, which is not congruent to 4 (modulo 3), so 9 is not in the sequence.
The 4th semiprime is 10, which is not congruent to 4 (modulo 4), so 10 is not in the sequence.
The 5th semiprime is 14, which is congruent to 4 (modulo 5), so 14 is in the sequence.
		

Links

• Lucas A. Brown, semiprimemods.py.

Crossrefs

Cf. A001358, A106129.

Formula

a(n) = A001358(A106129(n)).