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 A342927 #12 Mar 29 2021 15:06:10
%S A342927 3,4,3,5,4,7,5,9,4,10,11,12,7,5,14,8,15,9,17,4,10,19,20,11,21,22,8,24,
%T A342927 25,14,15,29,10,30,16,31,5,32,17,11,34,35,19,37,39,13,21,4,42,22,14,
%U A342927 44,23,45,8,47,25,50,51,17,54,28,55,29,57,4,30,59,60,31
%N A342927 The smallest polygonality of numbers that have exactly two different representations as polygonal numbers (A177029).
%H A342927 Michel Marcus, <a href="/A342927/b342927.txt">Table of n, a(n) for n = 1..10000</a>
%e A342927 6 is A177029(1); it is a 3-gonal and 6-gonal number; so a(1) = 3.
%e A342927 9 is A177029(2); it is a 4-gonal and 9-gonal number; so a(2) = 4.
%o A342927 (PARI) row(n) = my(v=List()); fordiv(2*n, k, if(k<2, next); if(k==n, break); my(s=(2*n/k-4+2*k)/(k-1)); if(denominator(s)==1, listput(v, s))); Vecrev(v); \\ A177028
%o A342927 lista(nn) = {for (n=3, nn, my(r = row(n)); if (#r == 2, print1(r[1], ", ")););}
%Y A342927 Cf. A177028, A177029, A342928.
%K A342927 nonn
%O A342927 1,1
%A A342927 _Michel Marcus_, Mar 29 2021