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.

A130152 Triangle read by rows: T(n,k) = number of permutations p of [n] such that max(|p(i)-i|)=k (n>=1, 0<=k<=n-1).

Original entry on oeis.org

1, 1, 1, 1, 2, 3, 1, 4, 9, 10, 1, 7, 23, 47, 42, 1, 12, 60, 157, 274, 216, 1, 20, 151, 503, 1227, 1818, 1320, 1, 33, 366, 1669, 4833, 10402, 13656, 9360, 1, 54, 877, 5472, 18827, 50879, 96090, 115080, 75600, 1, 88, 2088, 17531, 75693, 234061, 569602, 966456, 1077840, 685440, 1, 143, 4937, 55135, 304900, 1076807, 3111243, 6791994, 10553640, 11123280, 6894720
Offset: 1

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Author

Emeric Deutsch, May 27 2007

Keywords

Comments

Row sums are the factorials. T(n,n) = (n-2)!*(2n-3) = A007680(n-2) (for n>=2). T(n,1) = Fibonacci(n+1)-1 = A000071(n+1). Sum_{k=0..n-1} k*T(n,k) = A130153(n). For the statistic max(p(i)-i) see A056151.

Examples

			T(4,1) = 4 because we have 1243, 1324, 2134 and 2143.
Triangle starts:
  1;
  1,  1;
  1,  2,  3;
  1,  4,  9,  10;
  1,  7, 23,  47,  42;
  1, 12, 60, 157, 274, 216;
  ...
		

Crossrefs

Row sums give A000142.
T(n,floor(n/2)) gives A323807.

Programs

  • Maple
    with(combinat): for n from 1 to 7 do P:=permute(n): for i from 0 to n-1 do ct[i]:=0 od: for j from 1 to n! do if max(seq(abs(P[j][i]-i),i=1..n))=0 then ct[0]:=ct[0]+1 elif max(seq(abs(P[j][i]-i),i=1..n))=1 then ct[1]:=ct[1]+1 elif max(seq(abs(P[j][i]-i),i=1..n))=2 then ct[2]:=ct[2]+1 elif max(seq(abs(P[j][i]-i),i=1..n))=3 then ct[3]:=ct[3]+1 elif max(seq(abs(P[j][i]-i),i=1..n))=4 then ct[4]:=ct[4]+1 elif max(seq(abs(P[j][i]-i),i=1..n))=5 then ct[5]:=ct[5]+1 elif max(seq(abs(P[j][i]-i),i=1..n))=6 then ct[6]:=ct[6]+1 else fi od: a[n]:=seq(ct[i],i=0..n-1): od: for n from 1 to 7 do a[n] od; # a cumbersome program to obtain, by straightforward counting, the first 7 rows of the triangle
    n := 8: st := proc (p) max(seq(abs(p[j]-j), j = 1 .. nops(p))) end proc: with(combinat): P := permute(n): f := sort(add(t^st(P[i]), i = 1 .. factorial(n))); # program gives the row generating polynomial for the specified n - Emeric Deutsch, Aug 13 2009
    # second Maple program:
    b:= proc(s) option remember; (n-> `if`(n=0, 1, add((p-> add(
          coeff(p, x, i)*x^max(i, abs(n-j)), i=0..degree(p)))(
            b(s minus {j})), j=s)))(nops(s))
        end:
    T:= n-> (p-> seq(coeff(p, x, i), i=0..n-1))(b({$1..n})):
    seq(T(n), n=1..10);  # Alois P. Heinz, Jan 21 2019
    # third Maple program:
    A:= proc(n, k) option remember; LinearAlgebra[Permanent](
          Matrix(n, (i, j)-> `if`(abs(i-j)<=k, 1, 0)))
        end:
    T:= (n, k)-> A(n, k)-A(n, k-1):
    seq(seq(T(n, k), k=0..n-1), n=1..10);  # Alois P. Heinz, Jan 22 2019
  • Mathematica
    (* from second Maple program: *)
    b[s_List] := b[s] = Function[n, If[n == 0, 1, Sum[Function[p, Sum[ Coefficient[p, x, i]*x^Max[i, Abs[n - j]], {i, 0, Exponent[p, x]}]][b[s ~Complement~ {j}]], {j, s}]]][Length[s]];
    T[n_] := Function[p, Table[Coefficient[p, x, i], {i, 0, n-1}]][b[Range[n]] ];
    Table[T[n], {n, 1, 11}] // Flatten
    (* from third Maple program: *)
    A[n_, k_] := A[n, k] = Permanent[Table[If[Abs[i-j] <= k, 1, 0], {i, 1, n}, {j, 1, n}]];
    T[n_, k_] := A[n, k] - A[n, k - 1];
    Table[Table[T[n, k], {k, 0, n - 1}], {n, 1, 11}] // Flatten (* Jean-François Alcover, Dec 06 2019, after Alois P. Heinz *)

Formula

T(n,k) = A306209(n,k) - A306209(n,k-1) for k > 0, T(n,0) = 1. - Alois P. Heinz, Jan 29 2019

Extensions

More terms from R. J. Mathar, Oct 15 2007

A018927 For each permutation p of {1,2,...,n} define maxjump(p) = max(p(i) - i); a(n) is sum of maxjumps of all p.

Original entry on oeis.org

0, 1, 7, 45, 313, 2421, 20833, 198309, 2073793, 23664021, 292834513, 3907994949, 55967406433, 856355084661, 13944569166193, 240803714700069, 4395998055854593, 84596337986326101, 1711691067680320273, 36329581765125539589, 807099012174816776353
Offset: 1

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Author

Keywords

Crossrefs

Programs

  • Mathematica
    Table[Sum[k*k!*((k+1)^(n-k)-k^(n-k)),{k,0,n-1}],{n,1,20}] (* Vaclav Kotesovec, Mar 17 2014 *)

Formula

a(n) = Sum_{k=0..n-1} k*k!*((k+1)^(n-k)-k^(n-k)).
a(n) = Sum_{k=0..n*(n-1)/2} k*A127452(n-1,k). - Paul D. Hanna, Jan 15 2007
a(n) = Sum_{k=0..n-1} k * A180190(n,k). - Alois P. Heinz, Feb 21 2019

A129118 For each permutation p of {1,2,...,n} define minabsjump(p) = min(|p(i) - i|, 1<=i<=n); a(n) is the sum of minabsjumps of all p.

Original entry on oeis.org

0, 1, 2, 10, 48, 295, 2068, 16654, 150382, 1508500, 16631696, 199966907, 2603709640, 36501212971, 548150650582, 8779185528284, 149376644391508, 2690852138104504, 51161190374132154, 1023850096381041159, 21512688329462044264
Offset: 1

Views

Author

Keywords

Crossrefs

Programs

  • Maple
    n:=8; with(combinat); P:=permute(n); ct:= 0; for j to factorial(n) do ct:= ct+min(seq(abs(P[j][i]-i),i=1..n)) end do: ct; # yields a(n) for the specified n - Emeric Deutsch, Aug 24 2007
    # second Maple program:
    b:= proc(s) option remember; (n-> `if`(n=1, x^(s[]-1), add((p->
          add(coeff(p, x, i)*x^min(i, abs(n-j)), i=0..degree(p)))(
            b(s minus {j})), j=s)))(nops(s))
        end:
    a:= n-> (p-> add(coeff(p, x, i)*i, i=1..n-1))(b({$1..n})):
    seq(a(n), n=1..15);  # Alois P. Heinz, Jan 21 2019
  • Mathematica
    b[s_] := b[s] = Function[n, If[n == 1, x^(s - 1), Sum[Function[p, Sum[ SeriesCoefficient[p, {x, 0, i}]*x^Min[i, Abs[n - j]], {i, 0, Exponent[p, x]}]][b[s ~Complement~ {j}]], {j, s}]]][Length[s]] // Expand;
    a[n_] := a[n] = If[n == 1, 0, Function[p, Sum[SeriesCoefficient[p, {x, 0, i}]*i, {i, 1, n - 1}]][b[Range[n]][[1]]]];
    Table[Print[n, " ", a[n]]; a[n], {n, 1, 12}] (* Jean-François Alcover, May 21 2020, after 2nd Maple program *)

Formula

a(n) = Sum_{k=1..floor(n/2)} k * A299789(n,k). - Alois P. Heinz, Jan 21 2019

Extensions

One more term from Emeric Deutsch, Aug 24 2007
a(11)-a(13) from R. J. Mathar, Nov 01 2007
a(14) from Donovan Johnson, Sep 24 2010
a(15)-a(21) from Alois P. Heinz, Jan 21 2019
Showing 1-3 of 3 results.