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A322115 Regular triangle read by rows where T(n,k) is the number of unlabeled connected multigraphs with loops with n edges and k vertices. 9

%I

%S 1,1,1,1,2,1,1,4,4,2,1,6,11,9,3,1,9,25,34,20,6,1,12,52,104,99,49,11,1,

%T 16,94,274,387,298,118,23,1,20,162,645,1295,1428,881,300,47,1,25,263,

%U 1399,3809,5803,5088,2643,765,106,1,30,407,2823,10187,20645,24606,17872,7878,1998,235

%N Regular triangle read by rows where T(n,k) is the number of unlabeled connected multigraphs with loops with n edges and k vertices.

%H Andrew Howroyd, <a href="/A322115/b322115.txt">Table of n, a(n) for n = 0..1274</a>

%e Triangle begins:

%e 1

%e 1 1

%e 1 2 1

%e 1 4 4 2

%e 1 6 11 9 3

%e 1 9 25 34 20 6

%e 1 12 52 104 99 49 11

%o (PARI)

%o EulerT(v)={my(p=exp(x*Ser(dirmul(v,vector(#v,n,1/n))))-1); Vec(p/x,-#v)}

%o InvEulerMT(u)={my(n=#u, p=log(1+x*Ser(u)), vars=variables(p)); Vec(sum(i=1, n, moebius(i)*substvec(p + O(x*x^(n\i)), vars, apply(v->v^i,vars))/i) )}

%o permcount(v) = {my(m=1, s=0, k=0, t); for(i=1, #v, t=v[i]; k=if(i>1&&t==v[i-1], k+1, 1); m*=t*k; s+=t); s!/m}

%o edges(v,x)={sum(i=2, #v, sum(j=1, i-1, my(g=gcd(v[i],v[j])); g*x^(v[i]*v[j]/g))) + sum(i=1, #v, my(t=v[i]); ((t+1)\2)*x^t + if(t%2, 0, x^(t/2)))}

%o G(n,m)={my(s=0); forpart(p=n, s+=permcount(p)*EulerT(Vec(edges(p,x) + O(x*x^m), -m))); s/n!}

%o R(n)={Mat(apply(p->Col(p+O(y^n), -n), InvEulerMT(vector(n, k, 1 + y*Ser(G(k,n-1), y)))))}

%o { my(T=R(10)); for(n=1, #T, print(T[n, 1..n])) } \\ _Andrew Howroyd_, Nov 30 2018

%Y Row sums are A007719. Last column is A000055.

%Y Cf. A000664, A007716, A007718, A191646, A191970, A275421, A317533, A322114.

%K nonn,tabl

%O 0,5

%A _Gus Wiseman_, Nov 26 2018

%E Terms a(28) and beyond from _Andrew Howroyd_, Nov 30 2018

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Last modified August 11 23:45 EDT 2020. Contains 336434 sequences. (Running on oeis4.)