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 1-4 of 4 results.

A001383 Number of n-node rooted trees of height at most 3.

Original entry on oeis.org

1, 1, 1, 2, 4, 8, 15, 29, 53, 98, 177, 319, 565, 1001, 1749, 3047, 5264, 9054, 15467, 26320, 44532, 75054, 125904, 210413, 350215, 580901, 960035, 1581534, 2596913, 4251486, 6939635, 11296231, 18337815, 29692431, 47956995, 77271074, 124212966
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Comments

a(n+1) is also the number of n-vertex graphs that do not contain a P_4, C_4, or K_4 as induced subgraph (K_4-free trivially perfect graphs, cf. A123467). - Falk Hüffner, Jan 10 2016

References

  • 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

Crossrefs

Cf. A000041, A001383-A001385, A034823-A034826.

Programs

  • Maple
    s[ 2 ] := x/product('1-x^i','i'=1..30); # G.f. for trees of ht <=2, A000041
for k from 3 to 12 do # gets g.f. for trees of ht <= 3,4,5,...
s[ k ] := series(x/product('(1-x^i)^coeff(s[ k-1 ],x,i)','i'=1..30),x,31); od:
# For Maple program see link in A000235.
with(numtheory): etr:= proc(p) local b; b:=proc(n) option remember; local d,j; if n=0 then 1 else add(add(d*p(d), d=divisors(j)) *b(n-j), j=1..n)/n fi end end: A000041:= etr(n-> 1): a:= n->`if`(n=0,1, etr(k-> A000041(k-1))(n-1)): seq(a(n), n=0..40);  # Alois P. Heinz, Sep 08 2008
  • Mathematica
    m = 36; CoefficientList[ Series[x*Product[(1 - x^k)^(-PartitionsP[k - 1]), {k, 1, m}], {x, 0, m}], x] // Rest // Prepend[#, 1] & (* Jean-François Alcover, Jul 05 2011, after g.f. *)
  • PARI
    {a(n)=polcoeff(1+x*exp(sum(m=1,n,x^m/m/prod(k=1,n\m+1,1-x^(m*k)+x*O(x^n)))),n)} \\ Paul D. Hanna, Nov 01 2012

Formula

G.f.: S[ 3 ] := x*Product (1 - x^k)^(-p(k-1)), where p(k) = number of partitions of k.
a(n+1) is the Euler transform of p(n-1), where p() = A000041 is the partition function. - Franklin T. Adams-Watters, Mar 01 2006
G.f.: 1 + x*exp( Sum_{n>=1} x^n/n * Product_{k>=1} 1/(1 - x^(n*k)) ). - Paul D. Hanna, Nov 01 2012

A034824 Number of n-node rooted trees of height at most 7.

Original entry on oeis.org

1, 1, 1, 2, 4, 9, 20, 48, 115, 285, 710, 1789, 4514, 11431, 28922, 73182, 184917, 466755, 1176393, 2961205, 7443770, 18689435, 46869152, 117412440, 293832126, 734645046, 1835147741, 4580420719, 11423511895, 28469058647, 70899220083, 176449174539, 438854372942
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Links

Crossrefs

See A001383 for details.

Programs

  • Maple
    For Maple program see link in A000235.
with(numtheory): etr:= proc(p) local b; b:=proc(n) option remember; local d,j; if n=0 then 1 else add(add(d*p(d), d=divisors(j)) *b(n-j), j=1..n)/n fi end end: shr:= proc(p) n->`if`(n=0, 1,p(n-1)) end: b[0]:= etr(n->1): for j from 1 to 5 do b[j]:= etr(shr(b[j-1])) od: a:= shr(b[5]): seq(a(n), n=0..35); # Alois P. Heinz, Sep 08 2008
  • Mathematica
    Prepend[Nest[CoefficientList[Series[Product[1/(1-x^i)^#[[i]], {i, 1, Length[#]}], {x, 0, 40}], x]&, {1}, 7], 1] (* Geoffrey Critzer, Aug 01 2013 *)

Formula

Take Euler transform of A034823 and shift right. (Christian G. Bower).

A000393 Number of n-node rooted trees of height 6.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 1, 6, 26, 94, 308, 941, 2744, 7722, 21166, 56809, 149971, 390517, 1005491, 2564164, 6485901, 16289602, 40659669, 100934017, 249343899, 613286048, 1502515487, 3667953650, 8925161513, 21652815724, 52387028291
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

References

  • 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

Crossrefs

Column h=6 of A034781.

Programs

  • Maple
    For Maple program see link in A000235.
  • Mathematica
    f[n_] := Nest[CoefficientList[Series[Product[1/(1 - x^i)^#[[i]], {i, 1, Length[#]}], {x, 0, 40}], x] &, {1}, n];f[6]-f[5] (* Geoffrey Critzer, Aug 01 2013 *)

Formula

A034823-A001385. - Christian G. Bower

A000418 Number of n-node rooted trees of height 7.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 0, 1, 7, 34, 136, 487, 1615, 5079, 15349, 45009, 128899, 362266, 1002681, 2740448, 7411408, 19865445, 52840977, 139624510, 366803313, 958696860, 2494322662, 6463281890, 16686206047, 42935345688, 110142163940, 281763465941
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

References

  • 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

Crossrefs

Column h=7 of A034781.

Programs

  • Maple
    For Maple program see link in A000235.
  • Mathematica
    b[n_, i_, k_] := b[n, i, k] = If[n == 0, 1, If[i < 1 || k < 1, 0, Sum[ Binomial[b[i - 1, i - 1, k - 1] + j - 1, j]*b[n - i*j, i - 1, k], {j, 0, n/i}]]]; a[n_] := b[n - 1, n - 1, 7] - b[n - 1, n - 1, 6]; Array[a, 40] (* Jean-François Alcover, Feb 08 2016, after Alois P. Heinz in A034781 *)

Formula

A034824-A034823. - Christian G. Bower
Showing 1-4 of 4 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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