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 1-3 of 3 results.

A370484 Number T(n,k) of defective (binary) heaps on n elements from the set {0,1} with k defects; triangle T(n,k), n>=0, read by rows.

Original entry on oeis.org

1, 2, 3, 1, 5, 2, 1, 7, 6, 3, 11, 11, 9, 1, 16, 20, 24, 4, 26, 32, 52, 16, 2, 36, 60, 100, 52, 8, 56, 100, 192, 120, 40, 4, 81, 162, 351, 300, 111, 18, 1, 131, 255, 631, 627, 313, 77, 13, 1, 183, 427, 1067, 1311, 821, 241, 41, 5, 287, 692, 1856, 2484, 1894, 764, 184, 28, 3
Offset: 0

Views

Author

Alois P. Heinz, May 06 2024

Keywords

Comments

A defect in a defective heap is a parent-child pair not having the correct order.
T(n,k) is the number of bit vectors v of length n having exactly k indices i in [n] such that v[i] > v[floor(i/2)].
T(n,0) counts perfect (binary) heaps on n elements from the set {0,1}.
T(n,k) is defined for all n>=0 and k>=0. The triangle displays only positive terms. All other terms are zero.

Examples

			T(4,0) = 7: 0000, 1000, 1010, 1100, 1101, 1110, 1111.
T(4,1) = 6: 0001, 0010, 0100, 0101, 1001, 1011.
T(4,2) = 3: 0011, 0110, 0111.
(The examples use max-heaps.)
Triangle T(n,k) begins:
    1;
    2;
    3,   1;
    5,   2,    1;
    7,   6,    3;
   11,  11,    9,    1;
   16,  20,   24,    4;
   26,  32,   52,   16,   2;
   36,  60,  100,   52,   8;
   56, 100,  192,  120,  40,   4;
   81, 162,  351,  300, 111,  18,  1;
  131, 255,  631,  627, 313,  77, 13, 1;
  183, 427, 1067, 1311, 821, 241, 41, 5;
  ...
		

Crossrefs

Columns k=0-1 give: A091980(n+1), A372628.
Row sums give A000079.
T(2n,n) gives A372489.

Programs

  • Maple
    b:= proc(n, t) option remember; `if`(n=0, 1, (g-> (f->
          expand(b(f, 1)*b(n-1-f, 1)*t+b(f, x)*b(n-1-f, x)))(
          min(g-1, n-g/2)))(2^ilog2(n)))
        end:
    T:= n-> (p-> seq(coeff(p, x, i), i=0..degree(p)))(b(n, 1)):
    seq(T(n), n=0..15);
  • Mathematica
    b[n_, t_] := b[n, t] = If[n == 0, 1, Function[g, Function [f,
       Expand[b[f, 1]*b[n - 1 - f, 1]*t + b[f, x]*b[n - 1 - f, x]]][
       Min[g - 1, n - g/2]]][2^(Length[IntegerDigits[n, 2]] - 1)]];
    T[n_] := CoefficientList[b[n, 1], x];
    Table[T[n], {n, 0, 15}] // Flatten (* Jean-François Alcover, May 09 2024, after Alois P. Heinz *)

Formula

Sum_{k>=0} k * T(n,k) = A139756(n) = ceiling((n-1)*2^n/4).
Sum_{k>=0} (k+1) * T(n,k) = A045623(n) = ceiling((n+3)*2^n/4).

A323957 Number of defective (binary) heaps on n elements with exactly one defect.

Original entry on oeis.org

0, 1, 2, 9, 28, 90, 360, 1526, 7616, 32460, 190800, 947760, 6382464, 37065600, 296524800, 1812861600, 15283107840, 105015593280, 1017540576000, 7304720544000, 74472335308800, 629300251008000, 7429184791142400, 62417372203929600, 746041213793075200
Offset: 1

Views

Author

Alois P. Heinz, Feb 09 2019

Keywords

Comments

Or number of permutations p of [n] having exactly one index i in {1,...,n} such that p(i) > p(floor(i/2)).

Examples

			a(2) = 1: 12.
a(3) = 2: 213, 231.
a(4) = 9: 2413, 3124, 3214, 3241, 3412, 3421, 4123, 4132, 4213.
a(5) = 28: 25134, 25143, 35124, 35142, 35214, 35241, 42315, 42351, 43125, 43152, 43215, 43251, 43512, 43521, 45123, 45132, 45213, 45231, 45312, 45321, 52314, 52341, 52413, 52431, 53124, 53142, 53214, 53241.
a(6) = 90: 362451, 362541, 436125, 436215, ..., 652314, 652413, 653124, 653214.
(The examples use max-heaps.)
		

Crossrefs

Column k=1 of A306343.

Programs

  • Maple
    b:= proc(u, o) option remember; local n, g, l; n:= u+o;
          if n=0 then 1
        else g:= 2^ilog2(n); l:= min(g-1, n-g/2); expand(
             add(add(binomial(j-1, i)*binomial(n-j, l-i)*
             b(i, l-i)*b(j-1-i, n-l-j+i), i=0..min(j-1, l)), j=1..u)+
             add(add(binomial(j-1, i)*binomial(n-j, l-i)*
             b(l-i, i)*b(n-l-j+i, j-1-i), i=0..min(j-1, l)), j=1..o)*x)
          fi
        end:
    a:= n-> coeff(b(n, 0), x, 1):
    seq(a(n), n=1..25);
  • Mathematica
    b[u_, o_] := b[u, o] = Module[{n = u+o, g, l}, If[n == 0, 1,
         g = 2^(Length[IntegerDigits[n, 2]] - 1);
         l = Min[g - 1, n - g/2]; Expand[
         Sum[ Sum[Binomial[j - 1, i]*Binomial[n - j, l - i]*
         b[i, l-i]*b[j-1-i, n-l-j+i], {i, 0, Min[j-1, l]}], {j, 1, u}] +
         Sum[Sum[Binomial[j - 1, i]*Binomial[n - j, l - i]*
         b[l-i, i]*b[n-l-j+i, j-1-i], {i, 0, Min[j-1, l]}], {j, 1, o}]*x]]];
    a[n_] := Coefficient[b[n, 0], x, 1];
    Array[a, 25] (* Jean-François Alcover, Apr 22 2021, after Alois P. Heinz *)

A372643 Number of defective (binary) heaps on n elements from the set {0,1} where exactly one ancestor-successor pair does not have the correct order.

Original entry on oeis.org

0, 0, 1, 2, 4, 6, 13, 22, 36, 54, 99, 164, 260, 400, 692, 1146, 1730, 2638, 4358, 7148, 10788, 16716, 27168, 44692, 65630, 100736, 159851, 261156, 385740, 599704, 946368, 1551686, 2245014, 3455650, 5364990, 8743620, 12757292, 19869332, 30818816, 50429524
Offset: 0

Views

Author

Alois P. Heinz, May 08 2024

Keywords

Examples

			a(2) = 1: 01.
a(3) = 2: 001, 010.
a(4) = 4: 0010, 0100, 1001, 1011.
a(5) = 6: 00100, 01000, 10001, 10010, 10101, 10110.
a(6) = 13: 001000, 010000, 100001, 100010, 100100, 101010, 101011, 101100, 101101, 110001, 110011, 110101, 110111.
(The examples use max-heaps.)
		

Crossrefs

Column k=1 of A372640.

Programs

  • Maple
    b:= proc(n, t) option remember; convert(series(`if`(n=0, 1, (g->
          (f-> expand(b(f, t)*b(n-1-f, t)*x^t+b(f, t+1)*b(n-1-f, t+1)
               ))(min(g-1, n-g/2)))(2^ilog2(n))),x,2), polynom)
        end:
    a:= n-> coeff(b(n, 0),x,1):
    seq(a(n), n=0..39);
  • Mathematica
    b[n_, t_] := b[n, t] = If[n == 0, 1, Function[g, Function [f,
       Expand[b[f, t]*b[n - 1 - f, t]*x^t + b[f, t + 1]*b[n - 1 - f, t + 1]]][
       Min[g - 1, n - g/2]]][2^(Length@IntegerDigits[n, 2] - 1)]];
    a[n_] := Coefficient[b[n, 0], x, 1];
    Table[a[n], {n, 0, 39}] (* Jean-François Alcover, May 09 2024, after Alois P. Heinz *)

Formula

a(n) = A372640(n,1).
Showing 1-3 of 3 results.