%I #27 Jan 06 2024 22:58:44
%S 1,2,7,39,324,3839,62973,1402792,41946319,1673580047,88922215948,
%T 6297931501377,596303138919753,75787556639822258,12991109500044250083,
%U 3018313885461813882295,955168488432838276254520,413639698066068492610331231,246197679553110860511406200613,202212713843977008653180874488520
%N Number of chordal graphs on n vertices with a fixed perfect elimination ordering (e.g., 1,2,3,...,n)
%C 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 (PARI)
%o a(n)={
%o local(M=Map(Mat([1, 1])));
%o my(acc(p, v)=my(z); mapput(M, p, if(mapisdefined(M, p, &z), z+v, v)));
%o my(proc(p,m)=for(k=0, poldegree(p), acc(p + x*(1 + x)^k, polcoef(p,k)*m)));
%o for(r=1, n, my(src=Mat(M)); M=Map(); for(i=1, matsize(src)[1], proc(src[i, 1], src[i, 2])));
%o vecsum(Mat(M)[,2])
%o } \\ _Andrew Howroyd_, Jan 06 2024
%Y Cf. A048192.
%K nonn
%O 1,2
%A _Manfred Scheucher_ and _Robert Lauff_, Jan 05 2024
%E Terms a(12) and beyond from _Andrew Howroyd_, Jan 06 2024