login
A357808
Semiprimes k such that k is congruent to 4 modulo k's index in the sequence of semiprimes.
1
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
1,1
COMMENTS
a(28) > 8040423200947.
a(28) <= 1095927464608618, a(29) <= 1095927464608951 and a(38) <= 1095927464630173. - Martin Ehrenstein, Oct 28 2022
FORMULA
a(n) = A001358(A106129(n)).
EXAMPLE
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.
CROSSREFS
Sequence in context: A096003 A114058 A214901 * A365074 A284123 A135093
KEYWORD
nonn,hard,more
AUTHOR
Lucas A. Brown, Oct 13 2022
STATUS
approved