cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-7 of 7 results.

A050535 Number of loopless multigraphs on infinite set of nodes with n edges.

Original entry on oeis.org

1, 1, 3, 8, 23, 66, 212, 686, 2389, 8682, 33160, 132277, 550835, 2384411, 10709827, 49782637, 238998910, 1182772364, 6023860266, 31525780044, 169316000494, 932078457785, 5253664040426, 30290320077851, 178480713438362, 1073918172017297
Offset: 0

Views

Author

Vladeta Jovovic, Dec 29 1999

Keywords

Comments

Also, a(n) is the number of n-rowed binary matrices with all row sums equal to 2, up to row and column permutation (see Jovovic's formula). Also, a(n) is the limit of A192517(m,n) as m grows. - Max Alekseyev, Oct 18 2017
Row sums of the triangle defined by the Multiset Transformation of A076864,
1 ;
0 1;
0 2 1;
0 5 2 1;
0 12 8 2 1;
0 33 22 8 2 1;
0 103 72 26 8 2 1;
0 333 229 87 26 8 2 1;
0 1183 782 295 92 26 8 2 1;
0 4442 2760 1036 315 92 26 8 2 1;
0 17576 10270 3735 1129 321 92 26 8 2 1;
0 72810 39770 13976 4117 1154 321 92 26 8 2 1;
0 314595 160713 54132 15547 4237 1161 321 92 26 8 2 1;
- R. J. Mathar, Jul 18 2017
Also the number of non-isomorphic set multipartitions (multisets of sets) of {1, 1, 2, 2, 3, 3, ..., n, n}. - Gus Wiseman, Jul 18 2018

Examples

			From _Gus Wiseman_, Jul 18 2018: (Start)
Non-isomorphic representatives of the a(3) = 8 set multipartitions of {1, 1, 2, 2, 3, 3}:
  (123)(123)
  (1)(23)(123)
  (12)(13)(23)
  (1)(1)(23)(23)
  (1)(2)(3)(123)
  (1)(2)(13)(23)
  (1)(1)(2)(3)(23)
  (1)(1)(2)(2)(3)(3)
(End)
		

References

  • Frank Harary and Edgar M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 88, Eq. (4.1.18).

Crossrefs

Programs

Formula

a(n) = A192517(2*n,n) = A192517(m,n) for any m>=2*n. - Max Alekseyev, Oct 18 2017
Euler transform of A076864. - Andrew Howroyd, Oct 23 2019

Extensions

More terms from Sean A. Irvine, Oct 02 2011

A318951 Array read by rows: T(n,k) is the number of nonisomorphic n X n matrices with nonnegative integer entries and row sums k under row and column permutations, (n >= 1, k >= 0).

Original entry on oeis.org

1, 1, 1, 1, 2, 1, 1, 4, 3, 1, 1, 6, 14, 5, 1, 1, 9, 44, 53, 7, 1, 1, 12, 129, 458, 198, 11, 1, 1, 16, 316, 3411, 5929, 782, 15, 1, 1, 20, 714, 19865, 145168, 96073, 3111, 22, 1, 1, 25, 1452, 95214, 2459994, 9283247, 1863594, 12789, 30, 1, 1, 30, 2775, 383714, 30170387, 537001197, 833593500, 42430061, 53836, 42, 1
Offset: 1

Views

Author

Andrew Howroyd, Sep 05 2018

Keywords

Examples

			Array begins:
================================================================
n\k| 0  1    2       3         4            5              6
---|------------------------------------------------------------
1  | 1  1    1       1         1            1              1 ...
2  | 1  2    4       6         9           12             16 ...
3  | 1  3   14      44       129          316            714 ...
4  | 1  5   53     458      3411        19865          95214 ...
5  | 1  7  198    5929    145168      2459994       30170387 ...
6  | 1 11  782   96073   9283247    537001197    19578605324 ...
7  | 1 15 3111 1863594 833593500 189076534322 23361610029905 ...
...
		

Crossrefs

Rows 2..6 are A002620(n+2), A058389, A058390, A058391, A058392.

Programs

  • Mathematica
    permcount[v_List] := 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];
    K[q_List, t_, k_] := SeriesCoefficient[1/Product[g = GCD[t, q[[j]]]; (1 - x^(q[[j]]/g))^g, {j, 1, Length[q]}], {x, 0, k}];
    RowSumMats[n_, m_, k_] := Module[{s = 0}, Do[s += permcount[q]* SeriesCoefficient[Exp[Sum[K[q, t, k]/t*x^t, {t, 1, n}]], {x, 0, n}], {q, IntegerPartitions[m]}]; s/m!];
    Table[RowSumMats[n-k, n-k, k], {n, 1, 11}, {k, n-1, 0, -1}] // Flatten (* Jean-François Alcover, Sep 12 2018, after Andrew Howroyd *)
  • PARI
    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}
    K(q, t, k)={polcoeff(1/prod(j=1, #q, my(g=gcd(t, q[j])); (1 - x^(q[j]/g) + O(x*x^k))^g), k)}
    RowSumMats(n, m, k)={my(s=0); forpart(q=m, s+=permcount(q)*polcoeff(exp(sum(t=1, n, K(q, t, k)/t*x^t) + O(x*x^n)), n)); s/m!}
    for(n=1, 8, for(k=0, 6, print1(RowSumMats(n, n, k), ", ")); print)

A058391 Number of 5 X 5 matrices with nonnegative integer entries and all row sums equal to n, up to row and column permutation.

Original entry on oeis.org

1, 7, 198, 5929, 145168, 2459994, 30170387, 282159907, 2114430613, 13190940964, 70598379694, 331820068035, 1395291176641, 5327752138987, 18698405435444, 60922707883197, 185814239933254, 534246250634068, 1456622823771075
Offset: 0

Views

Author

Vladeta Jovovic, Nov 24 2000

Keywords

Crossrefs

Programs

A058390 Number of 4 X 4 matrices with nonnegative integer entries and all row sums equal to n, up to row and column permutation.

Original entry on oeis.org

1, 5, 53, 458, 3411, 19865, 95214, 383714, 1346183, 4202086, 11905966, 31061806, 75533056, 172800689, 374861365, 775978710, 1541027694, 2949003213, 5458806804, 9805626744, 17140511056
Offset: 0

Views

Author

Vladeta Jovovic, Nov 24 2000

Keywords

Crossrefs

Programs

A058392 Number of 6 X 6 matrices with nonnegative integer entries and all row sums equal to n, up to row and column permutation.

Original entry on oeis.org

1, 11, 782, 96073, 9283247, 537001197, 19578605324, 487615778173, 8892272235593, 125319645293555, 1423054983691408, 13451239365449764, 108603794657349271, 764673059329865921, 4775254548845993462, 26820549989969591853, 137072193873357150230, 643738505766475169048
Offset: 0

Views

Author

Vladeta Jovovic, Nov 24 2000

Keywords

Crossrefs

Programs

Extensions

Terms a(15) and beyond from Andrew Howroyd, Sep 05 2018

A058407 Number of 3 X n nonnegative integer matrices with all column sums 3, up to row and column permutation.

Original entry on oeis.org

1, 3, 13, 44, 134, 356, 876, 1966, 4146, 8236, 15592, 28252, 49357, 83377, 136837, 218728, 341554, 522064, 782810, 1153180, 1671698, 2387568, 3363738, 4679208, 6433183, 8748119, 11775343, 15699188, 20744108, 27180308, 35332850, 45588746
Offset: 0

Views

Author

Vladeta Jovovic, Nov 25 2000

Keywords

Comments

Number of 3 X n nonnegative integer matrices with all column sums equal to m, up to row and column permutation, is coefficient of x^n in expansion of 1 / 6 * (1 / (1 - x)^C(m + 2,2) + 3 / (1 - x)^floor((m + 2) / 2) / (1 - x^2)^(C(m + 2,2) - floor((m + 2) / 2)) / 2 + 2 / (1 - x)^(C(m + 2,2) - 3 * floor(C(m + 2,2) / 3)) / (1 - x^3)^floor(C(m + 2,2) / 3)).

Crossrefs

Formula

G.f.: 1/6*(1/(1-x)^10+3/(1-x)^2/(1-x^2)^4+2/(1-x)/(1-x^3)^3).

Extensions

More terms from Max Alekseyev, Jun 21 2011

A058408 Number of 3 X n nonnegative integer matrices with all column sums 4, up to row and column permutation.

Original entry on oeis.org

1, 4, 26, 129, 546, 2010, 6615, 19650, 53790, 137035, 328262, 745078, 1613072, 3348198, 6693822, 12937656, 24253200, 44219610, 78604130, 136511100, 232054284
Offset: 0

Views

Author

Vladeta Jovovic, Nov 25 2000

Keywords

Comments

Number of 3 X n nonnegative integer matrices with all column sums equal to m, up to row and column permutation, is coefficient of x^n in expansion of 1 / 6 * (1 / (1 - x)^C(m + 2,2) + 3 / (1 - x)^floor((m + 2) / 2) / (1 - x^2)^(C(m + 2,2) - floor((m + 2) / 2)) / 2 + 2 / (1 - x)^(C(m + 2,2) - 3 * floor(C(m + 2,2) / 3)) / (1 - x^3)^floor(C(m + 2,2) / 3)).

Crossrefs

Formula

G.f.: 1/6*(1/(1-x)^15+3/(1-x)^3/(1-x^2)^6+2/(1-x^3)^5).
Showing 1-7 of 7 results.