A357741 Semiprimes k such that k is divisible by its index in the sequence of semiprimes.

4, 6, 9, 21, 33, 129, 159, 3066835, 3067195, 3067255, 3067615, 3067745, 3068045, 44690978227, 44690978647, 44690978983, 44690979529

Offset: 1

Author

Lucas A. Brown, Oct 13 2022

Keywords

• nonn
• hard
• more

Comments

No further terms <= 8040423200947. - Lucas A. Brown, Oct 13 2022

Conjecture: a(18) > 10^17. - Martin Ehrenstein, Oct 28 2022

Examples

			The 1st semiprime is 4, which is divisible by 1, so 4 is in the sequence.
The 4th semiprime is 10, which is not divisible by 4, so 10 is not in the sequence.
The 7th semiprime is 21, which is divisible by 7, so 21 is in the sequence.
		

Links

• Lucas A. Brown, semiprimemods.py

Crossrefs

Cf. A001358, A106125, A356764.

Formula

a(n) = A001358(A106125(n))