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 A342469 #7 Mar 14 2021 07:00:11 %S A342469 1,3,4,5,6,9,10,12,15,16,21,22,25,28,35,36,45,49,51,55,64,66,70,78,81, %T A342469 91,92,100,105,117,120,121,136,144,145,153,169,171,176,190,196,210, %U A342469 225,231,247,253,256,276,287,289,300,324,325,330,351,361,376,378,400 %N A342469 Positive numbers that are triangular, square or pentagonal. %o A342469 (PARI) isok(m) = ispolygonal(m,3) || ispolygonal(m,4) || ispolygonal(m,5); %Y A342469 Cf. A000290, A000217, A000326, A005214. %Y A342469 Cf. A245646, A245647, A245648. %K A342469 nonn %O A342469 1,2 %A A342469 _Michel Marcus_, Mar 13 2021