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Semiprimes written in base 2.
3

%I #9 Oct 27 2024 20:29:14

%S 100,110,1001,1010,1110,1111,10101,10110,11001,11010,100001,100010,

%T 100011,100110,100111,101110,110001,110011,110111,111001,111010,

%U 111110,1000001,1000101,1001010,1001101,1010010,1010101,1010110,1010111,1011011,1011101,1011110,1011111

%N Semiprimes written in base 2.

%C Semiprime analog of A004676 Primes written in base 2. Partial sums are A122467; equivalently, this sequence is the first differences of A122467.

%F a(n) = A007088(A001358(n)).

%t lim=100;SP=Select[Range[lim],PrimeOmega[#]==2&];ll=Length[SP];Table[FromDigits[IntegerDigits[SP[[n]],2]],{n,ll}] (* _James C. McMahon_, Oct 27 2024 *)

%Y Cf. A001358, A007088, A004676, A122467.

%K base,easy,nonn

%O 1,1

%A _Jonathan Vos Post_, Sep 09 2006

%E a(31)-a(34) from _James C. McMahon_, Oct 27 2024