A092021 Numbers k such that k-th prime + k-th semiprime is semiprime.

1, 2, 3, 5, 7, 10, 15, 19, 22, 24, 26, 27, 31, 36, 41, 44, 57, 60, 67, 78, 84, 87, 91, 93, 101, 102, 103, 104, 105, 107, 115, 116, 120, 121, 124, 126, 128, 129, 131, 135, 136, 137, 138, 140, 151, 161, 168, 183, 186, 189, 190, 191, 195, 208, 215, 225, 227, 228, 231

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

3 is a member because third prime is 5, third semiprime is 9 and 5+9=14 is semiprime.

Maple

P:= select(isprime, [2, seq(i, i=3..10000, 2)]):
S:= select(t -> numtheory:-bigomega(t)=2, [$4..10000]):
select(t -> numtheory:-bigomega(P[t]+S[t]) = 2, [$1 .. min(nops(P), nops(S))]); # Robert Israel, Nov 15 2023

Crossrefs

Cf. A092108.

Sequence in context: A120446 A082531 A291298 * A022475 A330937 A011972

Adjacent sequences: A092018 A092019 A092020 * A092022 A092023 A092024

Keyword

easy,nonn

Author

Ray Chandler, Feb 24 2004

Status

approved