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 A217955 Triangular array read by rows.  T(n,k) is the number of unlabeled graphs on n nodes that have exactly k distinct components (n >= 1). 3
 1, 1, 2, 1, 6, 2, 21, 8, 112, 28, 2, 853, 145, 7, 11117, 1022, 34, 261080, 12320, 181, 1, 11716571, 274785, 1266, 12, 1006700565, 12007355, 14106, 63, 164059830476, 1019030127, 293756, 407, 50335907869219, 165091859656, 12362198, 3023, 6, 29003487462848061, 50502058491413, 1032671168, 33035, 51, 31397381142761241960, 29054157815353374, 166176421788, 645086, 399, 63969560113225176176277, 31426486309136268658, 50672459139597, 25830118, 3113 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Row sums are A207828. Column 1 is A001349. Column 2 is A216785. Column 3 is A058915. LINKS FORMULA O.g.f.: Product_{n>=1} (1 + y*x^n)^A001349(n). EXAMPLE Triangle begins          1;          1;          2,      1;          6,      2;         21,      8;        112,     28,    2;        853,    145,    7;      11117,   1022,   34;     261080,  12320,  181,  1;   11716571, 274785, 1266, 12; MATHEMATICA Needs["Combinatorica`"]; max=20; A000088=Table[NumberOfGraphs[n], {n, 0, max}]; f[x_]=1-Product[1/(1-x^k)^a[k], {k, 1, max}]; a[0]=a[1]=a[2]=1; coes=CoefficientList[Series[f[x], {x, 0, max}], x]; sol=First[Solve[Thread[Rest[coes+A000088]== 0]]]; cg=Table[a[n], {n, 1, max}]/.sol; CoefficientList[Series[Product[(1+y x^i)^cg[[i]], {i, 1, max}], {x, 0, max}], {x, y}]//Grid (* after code by Jean-François Alcover in A001349 *) CROSSREFS Sequence in context: A174421 A089849 A185330 * A325703 A321898 A284434 Adjacent sequences:  A217952 A217953 A217954 * A217956 A217957 A217958 KEYWORD nonn,tabf AUTHOR Geoffrey Critzer, Oct 15 2012 STATUS approved

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Last modified January 22 03:32 EST 2021. Contains 340360 sequences. (Running on oeis4.)