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.

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A036723 G.f. satisfies A(x) = 1 + x*cycle_index(G,A(x)) where G = cyclic group of order 2 generated by (1,2)(3,4).

Original entry on oeis.org

1, 1, 2, 8, 30, 135, 622, 3032, 15134, 77506, 403780, 2135588, 11430910, 61815916, 337193808, 1853183376, 10251612034, 57037706410, 318965425380, 1791842232154, 10107161112356, 57221612791015, 325045726349906, 1852055247196164
Offset: 0

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Author

Keywords

Crossrefs

A359392 Number of trees on n unlabeled nodes with all nodes of degree <= 7.

Original entry on oeis.org

1, 1, 1, 1, 2, 3, 6, 11, 23, 46, 104, 230, 539, 1270, 3081, 7536, 18785, 47207, 120074, 307739, 795426, 2069248, 5418014, 14263084, 37742929, 100331646, 267854040, 717863832, 1930888297, 5210968114, 14106844554
Offset: 0

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Author

Robert A. Russell, Dec 29 2022

Keywords

Crossrefs

Column k=7 of A144528; A036722 (rooted trees).

Programs

  • Mathematica
    n = 30; (* algorithm from Rains and Sloane *)
    m = 7; (* maximum degree of node *)
    CIm[f_, h_, x_] =  SymmetricGroupIndex[m-1, x] /. x[i_] -> f[h, x^i];
    CI[f_, h_, x_] = SymmetricGroupIndex[m, x] /. x[i_] -> f[h, x^i];
    T[-1, z_] := 1; T[h_, z_] :=  T[h, z] = Table[z^k, {k, 0, n}] .
      Take[CoefficientList[z^(n+1) + 1 + CIm[T, h-1, z] z, z], n+1];
    ReplacePart[Sum[Take[CoefficientList[z^(n+1) + CI[T, h-1, z] z - CI[T, h-2, z] z - (T[h-1, z] - T[h-2, z]) (T[h-1, z] - 1), z], n+1], {h, 1, n/2}] + PadRight[{0, 1}, n+1] + Sum[Take[CoefficientList[z^(n+1) + (T[h, z]
      - T[h-1, z])^2/2 + (T[h, z^2] - T[h-1, z^2])/2, z], n+1], {h, 0, n/2}],
      1->1] (* end of original program *)
    b[n_, i_, t_, k_] := b[n,i,t,k] = If[i<1, 0, Sum[Binomial[b[i-1,i-1,
      k,k] + j-1, j]* b[n-i*j, i-1, t-j, k], {j, 0, Min[t, n/i]}]];
    b[0, i_, t_, k_] = 1; m = 6; (* m = maximum children *) n = 40;
    gf[x_] = 1 + Sum[b[j-1,j-1,m,m]x^j,{j,1,n}]; (* G.f. for A036722 *)
    ci[x_] = SymmetricGroupIndex[m+1, x] /. x[i_] -> gf[x^i];
    CoefficientList[Normal[Series[gf[x] - (gf[x]^2 - gf[x^2])/2 + x ci[x],
    {x, 0, n}]],x] (* Robert A. Russell, Jan 19 2023 *)

Formula

G.f.: B(x) - cycle_index(S2,-B(x)) + x * cycle_index(S7,B(x)) = B(x) - (B(x)^2 - B(x^2)) / 2 + x * (B(x)^7 + 21 B(x)^5 B(x^2) + 105 B(x)^3 B(x^2)^2 + 105 B(x) B(x^2)^3 + 70 B(x)^4 B(x^3) + 420 B(x)^2 B(x^2) B(x^3) + 210 B(x^2)^2 B(x^3) + 280 B(x) B(x^3)^2 + 210 B(x)^3 B(x^4) + 630 B(x) B(x^2) B(x^4) + 420 B(x^3) B(x^4) + 504 B(x)^2 B(x^5) + 504 B(x^2) B(x^5) + 840 B(x) B(x^6) + 720 B(x^7)) / 5040, where B(x) = 1 + x * cycle_index(S6,B(x)) = 1 + x * (B(x)^6 + 15*B(x)^4*B(x^2) + 45*B(x)^2*B(x^2)^2 + 15*B(x^2)^3 + 40*B(x)^3*B(x^3) + 120*B(x)*B(x^2)*B(x^3) + 40*B(x^3)^2 + 90*B(x)^2*B(x^4) + 90*B(x^2)*B(x^4) + 144*B(x)*B(x^5) + 120*B(x^6)) / 720 is the generating function for A036722. - Robert A. Russell, Jan 19 2023
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