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A002862
Number of nonisomorphic connected functions with no fixed points, or proper rings with n edges.
(Formerly M1403 N0547)
5
0, 1, 2, 5, 11, 31, 77, 214, 576, 1592, 4375, 12183, 33864, 94741, 265461, 746372, 2102692, 5938630, 16803610, 47639902, 135288198, 384812502, 1096141974, 3126648842, 8929715592, 25533447030, 73090099586, 209438176485, 600721031344, 1724585494225
OFFSET
1,3
REFERENCES
R. A. Fisher, Contributions to Mathematical Statistics, Wiley, 1950, 41.399.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
R. K. Guy, Letter to N. J. A. Sloane, 1988-04-12 (annotated scanned copy) Includes illustrations for n <= 6.
MATHEMATICA
Needs["Combinatorica`"]; nn=30; s[n_, k_]:=s[n, k]=a[n+1-k]+If[n<2 k, 0, s[n-k, k]]; a[1]=1; a[n_]:=a[n]=Sum[a[i] s[n-1, i] i, {i, 1, n-1}]/(n-1); rt=Table[a[i], {i, 1, nn}]; cfd=Drop[Apply[Plus, Table[Take[CoefficientList[CycleIndex[CyclicGroup[n], s]/.Table[s[j]->Table[Sum[rt[[i]] x^(k*i), {i, 1, nn}], {k, 1, nn}][[j]], {j, 1, nn}], x], nn], {n, 2, 30}]], 1] (* Geoffrey Critzer, Oct 14 2012, after code given by Robert A. Russell in A000081 *)
CROSSREFS
(A002861) minus (A000081).
Sequence in context: A291139 A139467 A124481 * A190865 A275427 A139464
KEYWORD
nonn,nice
EXTENSIONS
More terms and better description from Christian G. Bower
STATUS
approved

  NODES
Community 1
Intern 1
os 2
text 2
web 1