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 A121040 #11 Feb 12 2017 21:52:13
%S A121040 20,120,200,220,320,420,520,620,720,820,920,1020,1120,1200,1220,1320,
%T A121040 1420,1520,1620,1720,1820,1920,2000,2020,2040,2060,2080,2120,2200,
%U A121040 2220,2320,2420,2520,2620,2720,2820,2920,3020,3120,3200,3220,3320,3420,3520
%N A121040 Multiples of 20 containing a 20 in their decimal representation.
%C A121040 Not the same as A044352.
%H A121040 <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>.
%F A121040 a(n) ~ 20n. - _Charles R Greathouse IV_, Feb 12 2017
%t A121040 Select[20*Range[200],SequenceCount[IntegerDigits[#],{2,0}]>0&] (* The program uses the SequenceCount function from Mathematica version 10 *) (* _Harvey P. Dale_, Nov 27 2015 *)
%o A121040 (PARI) is(n)=if(n%20, return(0)); while(n>19, if(n%100==20, return(1)); n\=10); 0 \\ _Charles R Greathouse IV_, Feb 12 2017
%Y A121040 Cf. A121041, A008602, A011531, A121022, A121023, A121024, A121025, A121026, A121027, A121028, A121029, A121030, A121031, A121032, A121033, A121034, A121035, A121036, A121037, A121038, A121039.
%K A121040 nonn,base,easy
%O A121040 1,1
%A A121040 _Reinhard Zumkeller_, Jul 21 2006
%E A121040 Corrected by _T. D. Noe_, Oct 25 2006