This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A054919 Number of nonisomorphic connected unlabeled binary relations on n nodes. 3
 1, 2, 7, 86, 2818, 285382, 96324549, 112087100482, 458071928280897, 6665704296529088252, 349377209492194571020053, 66602723163954144515240479674, 46557323273646194397778583902876038, 120168498151800396724425973133360413846262, 1152049915423012273792614840793828654424980146983 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Andrew Howroyd, Table of n, a(n) for n = 0..50 V. A. Liskovets, Some easily derivable sequences, J. Integer Sequences, 3 (2000), #00.2.2. FORMULA Inverse Euler transform of A000595. EXAMPLE Nonisomorphic connected relations on set {1,2} are {2r1}, {1r1,2r1}, {2r1,2r2}, {1r1,2r1,2r2}, {1r2,2r1}, {1r1,1r2,2r1}, {1r1,1r2,2r1,2r2} so a(2)=7. MATHEMATICA nn=7; c=Join[{1, 2}, Table[CycleIndex[Join[PairGroup[SymmetricGroup[n], Ordered], Permutations[Range[n^2-n+1, n^2]], 2], s] /. Table[s[i]->2, {i, 1, n^2-n}], {n, 2, nn}]]; f[x_]:=Sum[a[n]x^n, {n, 0, nn}]; b=Sum[c[[n+1]]x^n, {n, 0, nn}]; sol=SolveAlways[b==Normal[Series[Product[1/(1-x^i)^a[i], {i, 1, nn}], {x, 0, nn}]], x]; Table[a[n], {n, 1, nn}]/.sol (* Geoffrey Critzer, Mar 31 2013 *) CROSSREFS Cf. A000595. Sequence in context: A268299 A041291 A209331 * A119157 A079701 A096208 Adjacent sequences:  A054916 A054917 A054918 * A054920 A054921 A054922 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, May 24 2000 EXTENSIONS More terms from Vladeta Jovovic, Jul 16 2000 a(0)=1 prepended and a(13)-a(14) from Andrew Howroyd, Sep 10 2018 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 January 20 14:13 EST 2019. Contains 319333 sequences. (Running on oeis4.)