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 A019991 #20 Aug 02 2019 05:26:48 %S A019991 10,17,28,30,31,37,44,50,51,53,64,71,82,84,85,88,90,92,93,94,100,109, %T A019991 111,112,118,125,131,132,134,143,149,150,151,153,155,158,159,161,172, %U A019991 179,190,192,193,199,206,212,213,215,226,233,244,246,247,250 %N A019991 Indices n such that A307672(2*n) = 4. %C A019991 The original definition was: "A threequence, a 3-way partitioning of the integers: define a,b,c,A,B,C by a(0)=true, b(0)=c(0)=A(0)=B(0)=C(0)=false, a(n)=a(m) OR C(m) OR B(m), b(n)= b(m) OR A(m) OR C(m), c(n)= c(m) OR B(m) OR A(m), A(n)= A(m) OR b(m) OR c(m), B(n)= B(m) OR c(m) OR a(m), C(n)= C(m) OR a(m) OR b(m), where m = [ (n+1)/3 ]; sequence gives n such that c(2n) is true." - _Sean A. Irvine_, Apr 30 2019 %H A019991 R. W. Gosper, J. Z. Hunts, <a href="https://www.gathering4gardner.org/g4g10gift/math/Gosper_Bill-Strange_Series_for_Sierpinskis_Gasket.pdf">Strange Series for Sierpinski’s Gasket</a>, G4G10 Exchange Book, Vol. 2 (2012), 59-60. %Y A019991 Cf. A019989, A019990, A307672. %K A019991 nonn %O A019991 0,1 %A A019991 _Bill Gosper_ %E A019991 More terms from _Sean A. Irvine_, Apr 15 2019 %E A019991 New name from _Sean A. Irvine_, Apr 30 2019