A122466 Semiprimes written in base 2.

100, 110, 1001, 1010, 1110, 1111, 10101, 10110, 11001, 11010, 100001, 100010, 100011, 100110, 100111, 101110, 110001, 110011, 110111, 111001, 111010, 111110, 1000001, 1000101, 1001010, 1001101, 1010010, 1010101, 1010110, 1010111, 1011011, 1011101, 1011110, 1011111

Offset: 1

Author

Jonathan Vos Post, Sep 09 2006

Keywords

• base
• easy
• nonn

Comments

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

Crossrefs

Cf. A001358, A007088, A004676, A122467.

Programs

Mathematica

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 *)

Formula

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

Extensions

a(31)-a(34) from James C. McMahon, Oct 27 2024