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 A002862 Number of nonisomorphic connected functions with no fixed points, or proper rings with n edges. (Formerly M1403 N0547) 4
 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 (list; graph; refs; listen; history; text; internal format)
 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 Alois P. Heinz, Table of n, a(n) for n = 1..750 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 Adjacent sequences:  A002859 A002860 A002861 * A002863 A002864 A002865 KEYWORD nonn,nice AUTHOR EXTENSIONS More terms and better description from Christian G. Bower STATUS approved

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