A176193 The positions of semiprimes in A002808.

1, 2, 4, 5, 7, 8, 12, 13, 15, 16, 21, 22, 23, 25, 26, 31, 33, 35, 38, 40, 41, 43, 46, 49, 52, 55, 59, 61, 62, 63, 66, 68, 69, 70, 78, 81, 84, 87, 88, 90, 91, 92, 97, 100, 101, 106, 107, 108, 110, 111, 118, 120, 121, 123, 127, 129, 136, 137, 140, 142, 144, 149, 154, 155

Offset

1,2

Links

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

Formula

a(n) = A001358(n) - A000720(A001358(n)) - 1.

Maple

SP:= select(t -> numtheory:-bigomega(t) = 2, [$1..1000]):
map(t -> t - 1 - numtheory:-pi(t), SP); # Robert Israel, Jan 08 2024

Crossrefs

Cf. A000720, A001358, A002808.

Sequence in context: A261188 A343267 A350417 * A072920 A330708 A107899

Adjacent sequences: A176190 A176191 A176192 * A176194 A176195 A176196

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 11 2010

Extensions

Corrected (22, 41 inserted, 85 replaced by 87 etc.) by R. J. Mathar, Apr 13 2010

Status

approved