A008406 -id:A008406 - cp's OEIS frontend

A000220 Number of asymmetric trees with n nodes (also called identity trees).

1, 0, 0, 0, 0, 0, 1, 1, 3, 6, 15, 29, 67, 139, 310, 667, 1480, 3244, 7241, 16104, 36192, 81435, 184452, 418870, 955860, 2187664, 5025990, 11580130, 26765230, 62027433, 144133676, 335731381, 783859852, 1834104934, 4300433063, 10102854473, 23778351222

Offset: 1

N. J. A. Sloane

F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Camb. 1998, p. 330.
S. R. Finch, Mathematical Constants, Cambridge, 2003, p. 301 and 562.
F. Harary, Graph Theory. Addison-Wesley, Reading, MA, 1969, p. 232.
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 66, Eq. (3.3.22).
D. E. Knuth, Fundamental Algorithms, 3d Ed. 1997, pp. 386-88 describes methodology for generating similar sequence rapidly.
R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.
A. J. Schwenk, personal communication.
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).

Alois P. Heinz, Table of n, a(n) for n = 1..1000 (first 200 terms from T. D. Noe)
E. Friedman, Illustration of initial terms
F. Harary, R. W. Robinson and A. J. Schwenk, Twenty-step algorithm for determining the asymptotic number of trees of various species, J. Austral. Math. Soc., Series A, 20 (1975), 483-503. Errata: Vol. A 41 (1986), p. 325.
P. Leroux and B. Miloudi, Généralisations de la formule d'Otter, Ann. Sci. Math. Québec, Vol. 16, No. 1, pp. 53-80, 1992. (Annotated scanned copy)
A. J. Schwenk, Letter to N. J. A. Sloane, Aug 1972
Peter Steinbach, Field Guide to Simple Graphs, Volume 1, Part 17 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Peter Steinbach, Field Guide to Simple Graphs, Volume 3, Part 12 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Index entries for sequences related to trees

Cf. A000055, A000081.

Cf. A246169, A004111, A035056.

with(numtheory):
b:= proc(n) option remember; `if`(n<2, n, add(b(n-k)*add(
      b(d)*d*(-1)^(k/d+1), d=divisors(k)), k=1..n-1)/(n-1))
    end:
a:= n-> b(n)-(add(b(j)*b(n-j), j=0..n)+
       `if`(irem(n, 2)=0, b(n/2), 0))/2:
seq(a(n), n=1..50);  # Alois P. Heinz, Feb 24 2015

s[ n_, k_ ] := s[ n, k ]=a[ n+1-k ]+If[ n<2k, 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); Table[ a[ i ]-Sum[ a[ j ]a[ i-j ], {j, 1, i/2} ]+If[ OddQ[ i ], 0, a[ i/2 ](a[ i/2 ]-1)/2 ], {i, 1, 50} ] (* Robert A. Russell *)

G.f.: A(x)-A^2(x)/2-A(x^2)/2, where A(x) is g.f. for A004111.

a(n) ~ c * d^n / n^(5/2), where d = A246169 = 2.51754035263200389079535..., c = 0.29938828746578432274375484519722721162... . - Vaclav Kotesovec, Aug 25 2014

A003400 Number of asymmetric (not necessarily connected) graphs with n nodes.

Original entry on oeis.org

1, 0, 0, 0, 0, 8, 152, 3696, 135004, 7971848, 805364776, 144123121972

Offset: 1

N. J. A. Sloane

Number of simple graphs g on n nodes with |Aut(g)| = 1.

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 220, Section P3.4.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Klaus Brockhaus, The 6-node asymmetric graphs
Zoran Maksimovic, Number of graphs on n nodes whose automorphism group orders are k, n<=11
Yoav Spector, Moshe Schwartz, Study of potential Hamiltonians for quantum graphity, arXiv:1808.05632 [cond-mat.stat-mech], 2018.
Peter Steinbach, Field Guide to Simple Graphs, Volume 1, Part 17 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Eric Weisstein's World of Mathematics, Graph Automorphism
Eric Weisstein's World of Mathematics, Identity Graph

Cf. A124059 (connected simple asymmetric graphs).
Cf. A275867 (disconnected simple asymmetric graphs).
Cf. A000088 (simple graphs).

for n in {1..10}; do geng -q ${n} | countg -q -a1 | grep altogether | awk '{print $1}'; done # - Sean A. Irvine, Apr 22 2015

a(n) = A124059(n) + A275867(n).

a(8) and a(9) from Eric W. Weisstein, Jun 09 2004
a(10) and a(11) from Zoran Maksimovic, Vladeta Jovovic, Jan 21 2005
a(12) from Sean A. Irvine, Apr 22 2015

A192517 Table read by antidiagonals: T(n,k) = number of multigraphs with n vertices and k edges, with no loops allowed (n >= 1, k >= 0).

Original entry on oeis.org

1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1, 2, 1, 0, 1, 1, 3, 3, 1, 0, 1, 1, 3, 6, 4, 1, 0, 1, 1, 3, 7, 11, 5, 1, 0, 1, 1, 3, 8, 17, 18, 7, 1, 0, 1, 1, 3, 8, 21, 35, 32, 8, 1, 0, 1, 1, 3, 8, 22, 52, 76, 48, 10, 1, 0, 1, 1, 3, 8, 23, 60, 132, 149, 75, 12, 1, 0

Offset: 1

Alberto Tacchella, Jul 03 2011

Rows converge to sequence A050535, i.e. T(n,k) = A050535(k) for n >= 2k.

			Table begins:
[1,0,0,0,0,0,0,0,0,...],
[1,1,1,1,1,1,1,1,1,...],
[1,1,2,3,4,5,7,8,10,...],
[1,1,3,6,11,18,32,48,75,...],
[1,1,3,7,17,35,76,149,291,...],
[1,1,3,8,21,52,132,313,741,...],
[1,1,3,8,22,60,173,471,1303,...],
[1,1,3,8,23,64,197,588,1806,...],
...

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 171.

Andrew Howroyd, Table of n, a(n) for n = 1..1275 (terms 1..78 from Alberto Tacchella computed using nauty 2.4, terms 79..595 from Sean A. Irvine computed using cycle index method of Harary and Palmer).
R. J. Mathar, Statistics on Small Graphs, arXiv:1709.09000 [math.CO] (2017), Table 69.

Cf. A008406, A191646, A003082 (row 4), A014395 (row 5), A014396 (row 6).

\\ See A191646 for G function.
R(n)={Mat(vectorv(n, k, concat([1], G(k, n-1))))}
{ my(A=R(10)); for(n=1, #A, for(k=1, #A, print1(A[n,k], ", "));print) } \\ Andrew Howroyd, May 14 2018

A370167 Irregular triangle read by rows where T(n,k) is the number of unlabeled simple graphs covering n vertices with k = 0..binomial(n,2) edges.

Original entry on oeis.org

1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 2, 2, 1, 1, 0, 0, 0, 1, 4, 5, 5, 4, 2, 1, 1, 0, 0, 0, 1, 3, 9, 15, 20, 22, 20, 14, 9, 5, 2, 1, 1, 0, 0, 0, 0, 1, 6, 20, 41, 73, 110, 133, 139, 126, 95, 64, 40, 21, 10, 5, 2, 1, 1, 0, 0, 0, 0, 1, 3, 15, 50, 124, 271, 515, 832, 1181, 1460, 1581, 1516, 1291, 970, 658, 400, 220, 114, 56, 24, 11, 5, 2, 1, 1

Offset: 0

Gus Wiseman, Feb 15 2024

			Triangle begins:
  1
  0
  0  1
  0  0  1  1
  0  0  1  2  2  1  1
  0  0  0  1  4  5  5  4  2  1  1
  0  0  0  1  3  9 15 20 22 20 14  9  5  2  1  1

Andrew Howroyd, Table of n, a(n) for n = 0..1350 (rows 0..20)

Column sums are A000664.
Row sums are A002494.
This is the covering case of A008406, labeled A084546.
The labeled version is A054548, row sums A006129, column sums A121251.
The connected case is A054924, row sums A001349, column sums A002905.
The labeled connected case is A062734, with loops A369195.
The connected case with loops is A283755, row sums A054921.
The labeled version w/ loops is A369199, row sums A322661, col sums A173219.
Cf. A000666, A006125, A006649, A054547, A066383, A322700.

brute[m_]:=First[Sort[Table[Sort[Sort /@ (m/.Rule@@@Table[{(Union@@m)[[i]],p[[i]]},{i,Length[p]}])], {p,Permutations[Range[Length[Union@@m]]]}]]];
Table[Length[Union[brute /@ Select[Subsets[Subsets[Range[n],{2}],{k}],Union@@#==Range[n]&]]], {n,0,5},{k,0,Binomial[n,2]}]

\\ G(n) defined in A008406.
row(n)={Vecrev(G(n)-if(n>0, G(n-1)), binomial(n,2)+1)}
{ for(n=0, 7, print(row(n))) } \\ Andrew Howroyd, Feb 19 2024

a(42) onwards from Andrew Howroyd, Feb 19 2024

A000676 Number of centered trees with n nodes.

Original entry on oeis.org

1, 1, 0, 1, 1, 2, 3, 7, 12, 27, 55, 127, 284, 682, 1618, 3979, 9823, 24722, 62651, 160744, 415146, 1081107, 2831730, 7462542, 19764010, 52599053, 140580206, 377244482, 1016022191, 2745783463, 7443742141, 20239038700, 55178647926, 150820588425, 413226000775

Offset: 0

N. J. A. Sloane

A tree has either a center or a bicenter and either a centroid or a bicentroid. (These terms were introduced by Jordan.)
If the number of edges in a longest path in the tree is 2m, then the middle node in the path is the unique center, otherwise the two middle nodes in the path are the unique bicenters.
On the bottom of first page 266 of article Cayley (1881) is a table of A000676 and A000677 for n = 1..13. - Michael Somos, Aug 20 2018

			G.f. = 1 + x + x^3 + x^4 + 2*x^5 + 3*x^6 + 7*x^7 + 12*x^8 + 27*x^9 + 55*x^10 + ... - _Michael Somos_, Aug 20 2018

N. L. Biggs et al., Graph Theory 1736-1936, Oxford, 1976, p. 49.
F. Harary, Graph Theory, Addison-Wesley, Reading, MA, 1994; pp. 35, 36.
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).

Geoffrey Critzer, Table of n, a(n) for n = 0..200 (replacing the first version from N. J. A. Sloane)
Jean-François Alcover, Mathematica program
A. Cayley, On the analytical forms called trees, with application to the theory of chemical combinations, Reports British Assoc. Advance. Sci. 45 (1875), 257-305 = Math. Papers, Vol. 9, 427-460 (see p. 438).
A. Cayley, On the analytical forms called trees, Amer. J. Math., 4 (1881), 266-268.
C. Jordan, Sur les assemblages des lignes, J. Reine angew. Math., 70 (1869), 185-190.
E. M. Rains and N. J. A. Sloane, On Cayley's Enumeration of Alkanes (or 4-Valent Trees), J. Integer Sequences, Vol. 2 (1999), Article 99.1.1. [This articles states incorrectly that A000676 and A000677 give the numbers of trees with respectively a centroid and bicentroid.]
Peter Steinbach, Field Guide to Simple Graphs, Volume 1, Part 17 [but beware errors] (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Peter Steinbach, Field Guide to Simple Graphs, Volume 3, Part 12 [but beware errors] (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Eric Weisstein's World of Mathematics, Centered Tree.
Index entries for sequences related to trees.

Cf. A102911 (trees with a bicentroid), A027416 (trees with a centroid), A000677 (trees with a bicenter), A000055 (trees), A000081 (rooted trees).

Mathematica
```
(* See link. *)
```

a(n) + A000677(n) = A000055(n).

A275421 Triangle read by rows: T(n,k) = number of graphs with n edges and k connected components.

Original entry on oeis.org

1, 1, 1, 3, 1, 1, 5, 4, 1, 1, 12, 8, 4, 1, 1, 30, 23, 9, 4, 1, 1, 79, 57, 26, 9, 4, 1, 1, 227, 160, 68, 27, 9, 4, 1, 1, 710, 456, 197, 71, 27, 9, 4, 1, 1, 2322, 1402, 567, 208, 72, 27, 9, 4, 1, 1, 8071, 4468, 1748, 604, 211, 72, 27, 9, 4, 1, 1, 29503, 15071, 5555, 1874

Offset: 1

R. J. Mathar, Jul 27 2016

Multiset transformation of A002905.

			      1
      1     1
      3     1     1
      5     4     1     1
     12     8     4     1     1
     30    23     9     4     1     1
     79    57    26     9     4     1     1
    227   160    68    27     9     4     1     1
    710   456   197    71    27     9     4     1     1
   2322  1402   567   208    72    27     9     4     1     1
   8071  4468  1748   604   211    72    27     9     4     1     1
  29503 15071  5555  1874   615   212    72    27     9     4     1

Alois P. Heinz, Rows n = 1..60, flattened
Peter Steinbach, Field Guide to Simple Graphs, Volume 4, Table 1.1a, Part 1 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Index entries for triangles generated by the Multiset Transformation

Cf. A002905 (column 1), A000664 (row sums).

rows = 12;
A002905 = Import["https://oeis.org/A002905/b002905.txt", "Table"][[All, 2]];
gf = Product[(1 - y x^j)^-A002905[[j+1]], {j, 1, rows}];
Rest[CoefficientList[#, y]]& /@ Rest[CoefficientList[gf + O[x]^(rows+1), x]] // Flatten (* Jean-François Alcover, May 09 2019, after Alois P. Heinz *)

T(n,1) = A002905(n).

T(n,k) = Sum_{c_i*N_i=n,i=1..k} binomial(T(N_i,1)+c_i-1,c_i) for 1

G.f.: Product_{j>=1} (1-y*x^j)^(-A002905(j)). - Alois P. Heinz, Apr 13 2017

A000608 Number of connected partially ordered sets with n unlabeled elements.

Original entry on oeis.org

1, 1, 1, 3, 10, 44, 238, 1650, 14512, 163341, 2360719, 43944974, 1055019099, 32664984238, 1303143553205, 66900392672168, 4413439778321689

Offset: 0

N. J. A. Sloane, Simon Plouffe, J. A. Wright

K. K.-H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 4th S-E Conf. Combin., Graph Theory, Computing, Congress. Numer. 8 (1973), 169-184.
E. N. Gilbert, A catalog of partially ordered systems, unpublished memorandum, Aug 08, 1961.
G. Melançon, personal communication.
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).

Gunnar Brinkmann and Brendan D. McKay, Counting unlabeled topologies and transitive relations.
G. Brinkmann and B. D. McKay, Counting unlabeled topologies and transitive relations, J. Integer Sequences, Volume 8, 2005.
G. Brinkmann and B. D. McKay, Posets on up to 16 Points [On Brendan McKay's home page]
G. Brinkmann and B. D. McKay, Posets on up to 16 Points, Order 19 (2) (2002) 147-179.
K. K.-H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 4th S-E Conf. Combin., Graph Theory, Computing, Congress. Numer. 8 (1973), 169-184.
K. K.-H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 4th S-E Conf. Combin., Graph Theory, Computing, Congress. Numer. 8 (1973), 169-184. [Annotated scan of pages 180 and 183 only]
P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
E. N. Gilbert, A catalog of partially ordered systems, unpublished memorandum, Aug 08, 1961. [Annotated scanned copy]
Henry Sharp, Jr., Quasi-orderings and topologies on finite sets, Proceedings of the American Mathematical Society 17.6 (1966): 1344-1349. [Annotated scanned copy]
N. J. A. Sloane, List of sequences related to partial orders, circa 1972
N. J. A. Sloane, Transforms
Peter Steinbach, Field Guide to Simple Graphs, Volume 4, Part 10 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
N. L. White, Two letters to N. J. A. Sloane, 1970, with hand-drawn enclosure
Wikipedia, Illustration n=4, Illustration n=5, Illustration n=6" (2021)
J. A. Wright, There are 718 6-point topologies, quasiorderings and transgraphs, Preprint, 1970. [Annotated scanned copy]
J. A. Wright, There are 718 6-point topologies, quasi-orderings and transgraphs, Notices Amer. Math. Soc., 17 (1970), p. 646, Abstract #70T-A106.
J. A. Wright, Two related abstracts, 1970 and 1972 [Annotated scanned copies]
J. A. Wright, Letter to N. J. A. Sloane, Apr 06 1972, listing 18 sequences
Index entries for sequences related to posets

Inverse Euler transform of A000112.

Cf. A263864 (multiset transform), A342500 (refined by rank).

A000112 = Cases[Import["https://oeis.org/A000112/b000112.txt", "Table"], {, }][[All, 2]];
(* EulerInvTransform is defined in A022562 *)
{1} ~Join~ EulerInvTransform[Rest[A000112]] (* Jean-François Alcover, Dec 04 2019, updated Mar 17 2020 *)

More terms from Christian G. Bower, who pointed out connection with A000112, Jan 21 1998 and Dec 12 2001

More terms from Vladeta Jovovic, Jan 04 2006; corrected Jan 15 2006

A095133 Triangle of numbers of forests on n nodes containing k trees.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 3, 3, 2, 1, 1, 6, 6, 4, 2, 1, 1, 11, 11, 7, 4, 2, 1, 1, 23, 23, 14, 8, 4, 2, 1, 1, 47, 46, 29, 15, 8, 4, 2, 1, 1, 106, 99, 60, 32, 16, 8, 4, 2, 1, 1, 235, 216, 128, 66, 33, 16, 8, 4, 2, 1, 1, 551, 488, 284, 143, 69, 34, 16, 8, 4, 2, 1, 1, 1301, 1121, 636, 315, 149, 70, 34, 16, 8, 4, 2, 1, 1

Offset: 1

Eric W. Weisstein, May 29 2004

Row sums are A005195.

For k > n/2, T(n,k) = T(n-1,k-1). - Geoffrey Critzer, Oct 13 2012

			Triangle begins:
    1;
    1,  1;
    1,  1,  1;
    2,  2,  1,  1;
    3,  3,  2,  1,  1;
    6,  6,  4,  2,  1, 1;
   11, 11,  7,  4,  2, 1, 1;
   23, 23, 14,  8,  4, 2, 1, 1;
   47, 46, 29, 15,  8, 4, 2, 1, 1;
  106, 99, 60, 32, 16, 8, 4, 2, 1, 1;
  ...

Alois P. Heinz, Rows n = 1..141, flattened
Peter Steinbach, Field Guide to Simple Graphs, Volume 3, Part 12 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Peter Steinbach, Field Guide to Simple Graphs, Volume 4, Part 6 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
Eric Weisstein's World of Mathematics, Forest

Cf. A005195 (row sums), A005196, A106240, A000055 (first column), A274937 (2nd column), A105821.
Limiting sequence of reversed rows gives A215930.
Reflected table is A136605. - Alois P. Heinz, Apr 11 2014

with(numtheory):
b:= proc(n) option remember; local d, j; `if` (n<=1, n,
      (add(add(d*b(d), d=divisors(j)) *b(n-j), j=1..n-1))/(n-1))
    end:
t:= proc(n) option remember; local k; `if` (n=0, 1,
      b(n)-(add(b(k)*b(n-k), k=0..n)-`if`(irem(n, 2)=0, b(n/2), 0))/2)
    end:
g:= proc(n, i, p) option remember; `if`(p>n, 0, `if`(n=0, 1,
      `if`(min(i, p)<1, 0, add(g(n-i*j, i-1, p-j) *
       binomial(t(i)+j-1, j), j=0..min(n/i, p)))))
    end:
a:= (n, k)-> g(n, n, k):
seq(seq(a(n, k), k=1..n), n=1..14);  # Alois P. Heinz, Aug 20 2012

nn=30;s[n_,k_]:=s[n,k]=a[n+1-k]+If[n<2k,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);ft=Table[a[i]-Sum[a[j]a[i-j],{j,1,i/2}]+If[OddQ[i],0,a[i/2](a[i/2]+1)/2],{i,1,nn}];CoefficientList[Series[Product[1/(1-y x^i)^ft[[i]],{i,1,nn}],{x,0,20}],{x,y}]//Grid (* Geoffrey Critzer, Oct 13 2012, after code given by Robert A. Russell in A000055 *)

T(n, k) = sum over the partitions of n, 1M1 + 2M2 + ... + nMn, with exactly k parts, of Product_{i=1..n} binomial(A000055(i) + Mi - 1, Mi). - Washington Bomfim, May 12 2005

More terms from Vladeta Jovovic, Jun 03 2004

A070166 Irregular triangle read by rows giving T(n,k) = number of rooted graphs on n + 1 nodes with k edges (n >= 0, 0 <= k <= n(n-1)/2).

Original entry on oeis.org

1, 1, 1, 1, 2, 2, 1, 1, 2, 4, 6, 4, 2, 1, 1, 2, 5, 11, 17, 18, 17, 11, 5, 2, 1, 1, 2, 5, 13, 29, 52, 76, 94, 94, 76, 52, 29, 13, 5, 2, 1, 1, 2, 5, 14, 35, 83, 173, 308, 487, 666, 774, 774, 666, 487, 308, 173, 83, 35, 14, 5, 2, 1, 1, 2, 5, 14, 37, 98, 252, 585, 1239, 2396, 4135, 6340

Offset: 0

Vladeta Jovovic and Eric W. Weisstein, Apr 23 2002

T(n,k) is also the number of graphs with n nodes and k edges which may contain loops. (Delete the root node and change every edge leading to it into a loop.)

T(n,k) is also the number of symmetric relations with n points and k relations.

			Triangle begins:
1;
1, 1;
1, 2, 2, 1;
1, 2, 4, 6, 4, 2, 1;
1, 2, 5, 11, 17, 18, 17, 11, 5, 2, 1; <- gives either the numbers of rooted graphs on 5 nodes, or the numbers of graphs with loops on 4 nodes; with from 0 to 10 edges
1, 2, 5, 13, 29, 52, 76, 94, 94, 76, 52, 29, 13, 5, 2, 1;
...

E. Palmer and F. Harary, Graphical Enumeration, Academic Press, 1973.

Andrew Howroyd, Table of n, a(n) for n = 0..1560
Marko R. Riedel, Number of distinct connected digraphs
Eric Weisstein's World of Mathematics, Rooted Graphs

Row sums are A000666.

Cf. A054921, A008406, A283755, A322114, A368598, A368599.

Join[{{1},{1,1}},CoefficientList[Table[CycleIndex[Join[PairGroup[SymmetricGroup[n]],Permutations[Range[Binomial[n,2]+1,Binomial[n,2]+n]],2],s]/.Table[s[i]->1+x^i,{i,1,n^2-n}],{n,2,7}],x]]//Grid  (* Geoffrey Critzer, Oct 01 2012 *)
permcount[v_] := Module[{m = 1, s = 0, k = 0, t}, For[i = 1, i <= Length[v], i++, t = v[[i]]; k = If[i > 1 && t == v[[i - 1]], k + 1, 1]; m *= t*k; s += t]; s!/m];
edges[v_, t_] := Product[Product[g = GCD[v[[i]], v[[j]]]; t[v[[i]]*v[[j]]/g]^g, {j, 1, i - 1}], {i, 2, Length[v]}]*Product[c = v[[i]]; t[c]^Quotient[c + 1, 2]*If[OddQ[c], 1, t[c/2]], {i, 1, Length[v]}];
row[n_] := Module[{s = 0}, Do[s += permcount[p]*edges[p, 1 + x^# &], {p, IntegerPartitions[n]}]; s/n!] // Expand // CoefficientList[#, x] &
row /@ Range[0, 7] // Flatten (* Jean-François Alcover, Jan 07 2021, after Andrew Howroyd *)

permcount(v) = {my(m=1,s=0,k=0,t); for(i=1,#v,t=v[i]; k=if(i>1&&t==v[i-1],k+1,1); m*=t*k;s+=t); s!/m}
edges(v, t) = {prod(i=2, #v, prod(j=1, i-1, my(g=gcd(v[i], v[j])); t(v[i]*v[j]/g)^g )) * prod(i=1, #v, my(c=v[i]); t(c)^((c+1)\2)*if(c%2, 1, t(c/2)))}
G(n, A=0) = {my(s=0); forpart(p=n, s+=permcount(p)*edges(p, i->1+x^i+A)); s/n!}
{ for(n=0, 7, print(Vecrev(G(n)))) } \\ Andrew Howroyd, Oct 23 2019, updated Jan 09 2024

Offset changed by Andrew Howroyd, Oct 23 2019

A001433 Number of graphs with n nodes and n-1 edges.

Original entry on oeis.org

1, 1, 1, 3, 6, 15, 41, 115, 345, 1103, 3664, 12763, 46415, 175652, 691001, 2821116, 11932174, 52211412, 236007973, 1100528508, 5287050500, 26134330813, 132760735671, 692294900849, 3701754158688, 20275893222445, 113657560920970, 651449039159673, 3814790900995022, 22805438484189851

Offset: 1

N. J. A. Sloane

J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 146.
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).

Sean A. Irvine, Table of n, a(n) for n = 1..40
M. L. Stein and P. R. Stein, Enumeration of Linear Graphs and Connected Linear Graphs up to p = 18 Points. Report LA-3775, Los Alamos Scientific Laboratory of the University of California, Los Alamos, NM, Oct 1967

Cf. A008406.

Needs["Combinatorica`"]
Table[ NumberOfGraphs[n, n-1], {n, 1, 25}] (* Robert G. Wilson v *)
(* Second program (not needing Combinatorica): *)
permcount[v_] := Module[{m = 1, s = 0, k = 0, t}, For[i = 1, i <= Length[v], i++, t = v[[i]]; k = If[i > 1 && t == v[[i - 1]], k + 1, 1]; m *= t*k; s += t]; s!/m];
edges[v_, t_] := Product[Product[g = GCD[v[[i]], v[[j]]]; t[v[[i]]* v[[j]]/g]^g, {j, 1, i - 1}], {i, 2, Length[v]}]*Product[c = v[[i]]; t[c]^Quotient[c - 1, 2]*If[OddQ[c], 1, t[c/2]], {i, 1, Length[v]}];
a[n_] := a[n] = Module[{s = 0}, Do[s += permcount[p]*edges[p, 1 + x^# &], {p, IntegerPartitions[n]}]; s/n!] // Expand // SeriesCoefficient[#, {x, 0, n-1}]&;
Table[Print[n, " ", a[n]]; a[n], {n, 1, 35}] (* Jean-François Alcover, Aug 18 2022, after Andrew Howroyd in A008406 *)

More terms from Vladeta Jovovic, Jan 15 2000

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cp's OEIS Frontend

A000220 Number of asymmetric trees with n nodes (also called identity trees).

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Maple

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A003400 Number of asymmetric (not necessarily connected) graphs with n nodes.

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nauty

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A192517 Table read by antidiagonals: T(n,k) = number of multigraphs with n vertices and k edges, with no loops allowed (n >= 1, k >= 0).

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PARI

A370167 Irregular triangle read by rows where T(n,k) is the number of unlabeled simple graphs covering n vertices with k = 0..binomial(n,2) edges.

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Mathematica

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A000676 Number of centered trees with n nodes.

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A275421 Triangle read by rows: T(n,k) = number of graphs with n edges and k connected components.

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Mathematica

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A000608 Number of connected partially ordered sets with n unlabeled elements.

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Mathematica

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A095133 Triangle of numbers of forests on n nodes containing k trees.