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 A009129 #10 Feb 03 2018 21:32:33 %S A009129 60,84,90,120,132,144,168,180,210,240,252,264,270,280,288,300,312,330, %T A009129 336,360,390,396,408,420,432,440,450,456,462,468,480,504,510,520,528, %U A009129 540,546,552,560,570,576,588,600,612,616,624,630,660,672,680,684,690,700,720 %N A009129 Perimeter of more than one Pythagorean triangle. %H A009129 Charles R Greathouse IV, <a href="/A009129/b009129.txt">Table of n, a(n) for n = 1..10000</a> %o A009129 (PARI) is(k)=my(m2,mm2,s); for(m=2,sqrtint(k\2), m2=2*m; mm2=2*m^2; forstep(n=if(m%2,2,1),min(k\m2-m,m-1),m%2+1, if(k%(mm2+m2*n)==0 && gcd(m,n)==1 && s++>1, return(1)))); 0 \\ _Charles R Greathouse IV_, Feb 03 2018 %o A009129 (PARI) list(lim)=my(v=List(),ct=Map(),m2,mm2,t); for(m=2, sqrtint(lim\2), m2=2*m; mm2=2*m^2; forstep(n=if(m%2,2,1),min(lim\m2-m,m-1),m%2+1, if(gcd(m,n)>1, next); t=mm2+m2*n; forstep(k=t,lim,t, mapput(ct,k,mapisdefined(ct,k))))); for(n=60,lim, if(mapisdefined(ct,n) && mapget(ct,n), listput(v,n))); ct=0; Vec(v) \\ _Charles R Greathouse IV_, Feb 03 2018 %Y A009129 Subsequence of A010814. %K A009129 nonn %O A009129 1,1 %A A009129 _David W. Wilson_