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 A367448 #29 Jun 02 2025 15:27:24
%S A367448 1,2,7,39,324,3839,62973,1402792,41946319,1673580047,88922215948,
%T A367448 6297931501377,596303138919753,75787556639822258,12991109500044250083,
%U A367448 3018313885461813882295,955168488432838276254520,413639698066068492610331231,246197679553110860511406200613,202212713843977008653180874488520
%N A367448 Number of chordal graphs on n vertices with a fixed perfect elimination ordering (e.g., 1,2,3,...,n).
%C A367448 a(n) is the number of sign mappings X:([n] choose 2) -> {+,-} such that for any ordered 3-tuple a<b<c we have X(ab)X(ac)X(bc) not equal to -++.
%o A367448 (PARI)
%o A367448 a(n)={
%o A367448 local(M=Map(Mat([1, 1])));
%o A367448 my(acc(p, v)=my(z); mapput(M, p, if(mapisdefined(M, p, &z), z+v, v)));
%o A367448 my(proc(p,m)=for(k=0, poldegree(p), acc(p + x*(1 + x)^k, polcoef(p,k)*m)));
%o A367448 for(r=1, n, my(src=Mat(M)); M=Map(); for(i=1, matsize(src)[1], proc(src[i, 1], src[i, 2])));
%o A367448 vecsum(Mat(M)[,2])
%o A367448 } \\ _Andrew Howroyd_, Jan 06 2024
%Y A367448 Cf. A048192.
%K A367448 nonn
%O A367448 1,2
%A A367448 _Manfred Scheucher_ and _Robert Lauff_, Jan 05 2024
%E A367448 Terms a(12) and beyond from _Andrew Howroyd_, Jan 06 2024