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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

Table of n, a(n) for n=1..53.

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-Fran├žois 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.)