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 A212819 #15 Feb 16 2025 08:33:17
%S A212819 0,5,51,507,5047,50144,500265,5000421,50001942,500012608,5000058013,
%T A212819 50000171112,500000261313,5000000483289
%N A212819 Numbers up to 10^n with an odd number of prime factors, or negative Liouville function.
%H A212819 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LiouvilleFunction.html">Liouville Function</a>
%F A212819 a(n) = A011557(n) - A212818(n).
%F A212819 a(n) = (10^n)/2 - A090410(n)/2. - _Donovan Johnson_, May 30 2012
%F A212819 a(n) = A055038(10^n). - _Ray Chandler_, May 30 2012
%e A212819 a(1) = 5 since up to 10 there are the five numbers 2, 3, 5, 7, 8 with an odd number of prime factors or negative Liouville function.
%p A212819 zg:=0: zu:=0: G:=[]: U:=[]: k:=0:
%p A212819 for i from 1 to 10^8 do if numtheory[bigomega](i) mod 2 = 0 then zg:=zg+1: else zu:=zu+1: fi: if i=10^k then G:=[op(G),zg]: U:=[op(U),zu]: k:=k+1: fi: od:
%p A212819 print(U);
%t A212819 Table[Count[LiouvilleLambda[Range[10^n]], -1], {n, 0, 5}] (* _Ray Chandler_, May 30 2012 *)
%Y A212819 Cf. A002819, A008836, A026424, A066829, A090410.
%K A212819 nonn
%O A212819 0,2
%A A212819 _Martin Renner_, May 28 2012
%E A212819 a(9)-a(13) from _Donovan Johnson_, May 30 2012