A176193 - OEIS

%I #13 Jan 08 2024 18:22:56

%S 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,

%T 55,59,61,62,63,66,68,69,70,78,81,84,87,88,90,91,92,97,100,101,106,

%U 107,108,110,111,118,120,121,123,127,129,136,137,140,142,144,149,154,155

%N The positions of semiprimes in A002808.

%H Robert Israel, <a href="/A176193/b176193.txt">Table of n, a(n) for n = 1..10000</a>

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

%p SP:= select(t -> numtheory:-bigomega(t) = 2, [$1..1000]):

%p map(t -> t - 1 - numtheory:-pi(t), SP); # _Robert Israel_, Jan 08 2024

%Y Cf. A000720, A001358, A002808.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Apr 11 2010

%E Corrected (22, 41 inserted, 85 replaced by 87 etc.) by _R. J. Mathar_, Apr 13 2010