This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A362318 #27 Apr 24 2023 09:58:54
%S A362318 0,0,0,0,2,2,7,13,27,52,104,210,398,807,1542,3046,5936,11565,22584,
%T A362318 44012,86062,167786,327936,640630,1252327,2448518,4791344,9378159,
%U A362318 18364095,35979682,70515477,138275503,271246674,532304906,1045047118,2052464984,4032502528
%N A362318 Number of odd semiprimes between 2^(n-1) and 2^n.
%C A362318 This is the number of odd integers with precisely n bits that are the product of two (possibly identical) prime factors.
%C A362318 Odd numbers with two prime factors are used as the modulus in the RSA algorithm. This sequence gives the number of "candidate" RSA moduli having precisely n bits. Note that many of these candidates would not be suitable for cryptographic applications because they are easily factored.
%H A362318 Chai Wah Wu, <a href="/A362318/b362318.txt">Table of n, a(n) for n = 0..63 (using data in A120033 and A036378) </a>
%F A362318 a(n) = A362042(n) - A362042(n-1) for n>=1.
%F A362318 a(n) = A120033(n-1) - A036378(n-2) for n > 1. - _Chai Wah Wu_, Apr 24 2023
%t A362318 a[n_] := Length@Select[Range[2^(n - 1) + 1, 2^n - 1, 2], Total[Last /@ FactorInteger[#]] ==2 &]Table[a[n],{n,0,25}]
%Y A362318 Cf. A036378, A046315, A120033, A362042.
%K A362318 nonn
%O A362318 0,5
%A A362318 _Sidney Cadot_, Apr 16 2023
%E A362318 More terms from _Chai Wah Wu_, Apr 24 2023 (using data in A120033 and A036378)