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A259471
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Triangle read by rows: T(n,k) is the number of semi-regular relations on n nodes with each node having out-degree k (0 <= k <= n).
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3
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1, 1, 1, 1, 3, 1, 1, 7, 7, 1, 1, 19, 66, 19, 1, 1, 47, 916, 916, 47, 1, 1, 130, 16816, 91212, 16816, 130, 1, 1, 343, 373630, 12888450, 12888450, 373630, 343, 1, 1, 951, 9727010, 2411213698, 14334255100, 2411213698, 9727010, 951, 1, 1, 2615, 289374391, 575737451509, 22080097881081, 22080097881081, 575737451509, 289374391, 2615, 1
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OFFSET
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0,5
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LINKS
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FORMULA
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EXAMPLE
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Triangle begins:
1;
1, 1;
1, 3, 1;
1, 7, 7, 1;
1, 19, 66, 19, 1;
1, 47, 916, 916, 47, 1;
1, 130, 16816, 91212, 16816, 130, 1;
...
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MATHEMATICA
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permcount[v_] := Module[{m = 1, s = 0, k = 0, t}, For[i = 1, i <= Length[v], i++, t = v[[i]]; k = If[i > 1 && t == v[[i - 1]], k + 1, 1]; m *= t*k; s += t]; s!/m];
edges[v_, k_] := Product[SeriesCoefficient[Product[g = GCD[v[[i]], v[[j]] ]; (1 + x^(v[[j]]/g) + O[x]^(k + 1))^g, {j, 1, Length[v]}], {x, 0, k}], {i, 1, Length[v]}];
T[n_, k_] := Module[{s = 0}, Do[s += permcount[p]*edges[p, k], {p, IntegerPartitions[n]}]; s/n!];
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PROG
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(PARI)
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}
edges(v, k)={prod(i=1, #v, polcoef(prod(j=1, #v, my(g=gcd(v[i], v[j])); (1 + x^(v[j]/g) + O(x*x^k))^g), k))}
T(n, k)={my(s=0); forpart(p=n, s+=permcount(p)*edges(p, k)); s/n!} \\ Andrew Howroyd, Sep 13 2020
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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