login
A357741
Semiprimes k such that k is divisible by its index in the sequence of semiprimes.
2
4, 6, 9, 21, 33, 129, 159, 3066835, 3067195, 3067255, 3067615, 3067745, 3068045, 44690978227, 44690978647, 44690978983, 44690979529
OFFSET
1,1
COMMENTS
No further terms <= 8040423200947. - Lucas A. Brown, Oct 13 2022
Conjecture: a(18) > 10^17. - Martin Ehrenstein, Oct 28 2022
FORMULA
a(n) = A001358(A106125(n))
EXAMPLE
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.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Lucas A. Brown, Oct 13 2022
STATUS
approved