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 A243903 #13 Jun 14 2014 13:38:30
%S A243903 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,29,
%T A243903 30,31,32,33
%N A243903 Numbers n such that (number of primes <= n) is greater than or equal to (number of semiprimes <= n).
%C A243903 Conjecture: there are no additional terms.
%C A243903 We know from the asymptotic formulas (see Landau) that the sequence is finite. See also the graph of A243906. - _N. J. A. Sloane_, Jun 14 2014
%D A243903 E. Landau, Handbuch der Lehre von der Verteilung der Primzahlen, vol. 1, Teubner, Leipzig, 1909; third edition : Chelsea, New York (1974).
%t A243903 With[{nn=5000},Flatten[Position[Thread[{Accumulate[Table[ If[ PrimeOmega[n] == 2,1,0],{n,nn}]],PrimePi[Range[nn]]}],_?(Last[#]>=First[#]&),{1}, Heads-> False]]]
%Y A243903 Cf. A000040, A000720, A001358, A072000, A243906.
%K A243903 nonn
%O A243903 1,2
%A A243903 _Harvey P. Dale_, Jun 14 2014