The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A058915 Number of graphs with 3 distinct components. 2
 2, 7, 34, 181, 1266, 14106, 293756, 12362198, 1032671168, 166176421788, 50672459139597, 29105501987344357, 31455795559882541775, 64032588337815572241795, 246000022800939308314311897 (list; graph; refs; listen; history; text; internal format)
 OFFSET 6,1 REFERENCES F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, page 48, (2.6.3). LINKS FORMULA G.f.: 1/6*(f(x)^3 - 3*f(x)*f(x^2) + 2*f(x^3)), where f(x) = g(x) - 1 and g(x) is g.f. for connected graphs. Cf. A001349. MATHEMATICA Needs["Combinatorica`"]; max=25; 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; Take[CoefficientList[CycleIndex[AlternatingGroup[3], s]-CycleIndex[SymmetricGroup[3], s]/.Table[s[j]->Table[Sum[cg[[i]] x^(k*i), {i, 1, max}], {k, 1, max}][[j]], {j, 1, 3}], x], {7, max}] (* Geoffrey Critzer, Oct 15 2012; after code by Jean-François Alcover in A001349 *) CROSSREFS Cf. A001349. Column 3 of A217955. Sequence in context: A222940 A227120 A023053 * A273030 A020054 A206240 Adjacent sequences:  A058912 A058913 A058914 * A058916 A058917 A058918 KEYWORD easy,nonn AUTHOR Vladeta Jovovic, Jan 11 2001 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 26 16:27 EST 2020. Contains 338641 sequences. (Running on oeis4.)