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.

Previous Showing 51-58 of 58 results.

A123148 Triangle read by rows: T(n,k) is the coefficient of x^k in the polynomial p(n,x) defined by p(0,x) = -1, p(1,x) = x-2, p(n,x) = -x*p(n-1,x) + 2*p(n-2,x) for n >= 3 and 0 <= k <= n.

Original entry on oeis.org

-1, -2, 1, -2, 2, -1, -4, 4, -2, 1, -4, 8, -6, 2, -1, -8, 12, -12, 8, -2, 1, -8, 24, -24, 16, -10, 2, -1, -16, 32, -48, 40, -20, 12, -2, 1, -16, 64, -80, 80, -60, 24, -14, 2, -1, -32, 80, -160, 160, -120, 84, -28, 16, -2, 1, -32, 160, -240, 320, -280, 168, -112, 32, -18, 2, -1
Offset: 0

Views

Author

Roger L. Bagula, Oct 01 2006

Keywords

Examples

			The first few polynomials, p(n,x), are:
  p(0,x) = -1;
  p(1,x) = -2 +   x;
  p(2,x) = -2 + 2*x -   x^2;
  p(3,x) = -4 + 4*x - 2*x^2 +   x^3;
  p(4,x) = -4 + 8*x - 6*x^2 + 2*x^3 - x^4;
The triangle, T(n, k) = [x^k] p(n, x), begins as:
  -1;
  -2,  1;
  -2,  2,  -1;
  -4,  4,  -2,  1;
  -4,  8,  -6,  2,  -1;
  -8, 12, -12,  8,  -2,  1;
  -8, 24, -24, 16, -10,  2, -1;
		

Crossrefs

Programs

  • Magma
    A123148:=func< n,k | (-1)^(k+1)*2^Floor((n-k+1)/2)*Binomial( Floor((n+k)/2), k) >;
    [A123148(n,k): k in [0..n], n in [0..12]]; // G. C. Greubel, Jul 17 2023
    
  • Maple
    p[0]:=-1: p[1]:=x-2: for n from 2 to 10 do p[n]:=sort(expand(-x*p[n-1]+2*p[n-2])) od: for n from 0 to 10 do seq(coeff(p[n],x,k),k=0..n) od; # yields sequence in triangular form
  • Mathematica
    p[0,x]= -1; p[1,x]= x-2; p[k_, x_]:= p[k,x]= -x*p[k-1,x] + 2*p[k-2,x];
    T[n_, k_]:= Coefficient[p[n, x], x, k];
    Table[T[n,k], {n,0,12},{k,0,n}]//Flatten
  • SageMath
    def A123148(n,k): return (-1)^(k+1)*2^((n-k+1)//2)*binomial((n+k)//2, k)
    flatten([[A123148(n,k) for k in range(n+1)] for n in range(13)]) # G. C. Greubel, Jul 17 2023

Formula

T(n, k) = [x^k]( p(n,x) ), where p(0,x) = -1, p(1,x) = x-2, p(n,x) = -x*p(n-1,x) + 2*p(n-2,x).
Sum_{k=0..n} T(n, k) = -1.
Sum_{k=0..n} (-1)^k * T(n,k) = -A001045(n+2).
From G. C. Greubel, Jul 17 2023: (Start)
T(n,k) = (-1)^(k+1)*2^Floor((n-k+1)/2)*Binomial( Floor((n+k)/2), k).
T(n,k) = (-1)^(k+1)*2^Floor((n-k+1)/2)*A046854(n,k).
T(n,0) = -A016116(n+1).
T(n,1) = A171647(n).
Sum_{k=0..n} (-1)^k * abs(T(n,k)) = 1.
Sum_{k=0..floor(n/2)} T(n-k,k) = - A000034(n).
Sum_{k=0..floor(n/2)} (-1)^k*T(n-k,k) = -A038754(n). (End)

Extensions

Edited by N. J. A. Sloane, Oct 29 2006

A126127 Inverse square of A061554.

Original entry on oeis.org

1, -2, 1, -1, -2, 1, 5, -3, -2, 1, 2, 9, -5, -2, 1, -13, 9, 13, -7, -2, 1, -5, -33, 20, 17, -9, -2, 1, 34, -27, -61, 35, 21, -11, -2, 1, 13, 111, -73, -97, 54, 25, -13, -2, 1, -89, 80, 248, -151, -141, 77, 29, -15, -2, 1, -34, -355, 252, 461, -269, -193, 104, 33, -17, -2, 1
Offset: 0

Views

Author

Gary W. Adamson, Dec 17 2006

Keywords

Comments

Inverse of A061554 = A046854; therefore A126127 = (A046854)^2.

Examples

			First few rows of the triangle are:
1;
-2, 1;
-1, -2, 1;
5, -3, -2, 1;
2, 9, -5, -2, 1;
-13, 9, 13, -7, -2, 1;
...
		

Crossrefs

Programs

  • Maple
    T:= Matrix(20,20,(n,k) -> binomial(n-1, floor((n)/2 - (-1)^(n-k)*(k)/2)), shape=triangular[lower]):
    A:= T^(-2):
    seq(seq(A[i,k],k=1..i),i=1..20); # Robert Israel, Jul 07 2019

Formula

Given M = Pascal's triangle with descending row terms, (A061554); A126127 = M^(-2).
G.f. as triangle (conjectured): (1-x)*(1-x+x^2)/(1-x*y+3*x^2-x^3*y+x^4). - Robert Israel, Jul 07 2019

A153764 Triangle T(n,k), 0 <= k <= n, read by rows, given by [1,0,-1,0,0,0,0,0,0,0,0,...] DELTA [0,1,0,0,0,0,0,0,0,0,...] where DELTA is the operator defined in A084938.

Original entry on oeis.org

1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 2, 1, 1, 0, 1, 2, 3, 1, 1, 0, 1, 3, 3, 4, 1, 1, 0, 1, 3, 6, 4, 5, 1, 1, 0, 1, 4, 6, 10, 5, 6, 1, 1, 0, 1, 4, 10, 10, 15, 6, 7, 1, 1, 0, 1, 5, 10, 20, 15, 21, 7, 8, 1, 1, 0, 1, 5, 15, 20, 35, 21, 28, 8, 9, 1, 1, 0, 1, 6, 15, 35, 35, 56, 28, 36, 9, 10, 1, 1, 0
Offset: 0

Views

Author

Philippe Deléham, Jan 01 2009

Keywords

Comments

A130595*A153342 as infinite lower triangular matrices. Reflected version of A103631. Another version of A046854. Row sums are Fibonacci numbers (A000045).
A055830*A130595 as infinite lower triangular matrices.

Examples

			Triangle begins:
  1;
  1, 0;
  1, 1, 0;
  1, 1, 1, 0;
  1, 2, 1, 1, 0;
  1, 2, 3, 1, 1, 0;
  1, 3, 3, 4, 1, 1, 0;
  ...
		

Crossrefs

Programs

  • Magma
    /* As triangle */ [[Binomial(Floor((n+k-1)/2),k): k in [0..n]]: n in [0.. 15]]; // Vincenzo Librandi, Aug 28 2016
  • Mathematica
    Table[Binomial[Floor[(n + k - 1)/2], k], {n, 0, 45}, {k, 0, n}] // Flatten (* G. C. Greubel, Aug 27 2016 *)

Formula

T(n,k) = binomial(floor((n+k-1)/2),k).
Sum_{k=0..n} T(n,k)*x^k = A122335(n-1), A039834(n-2), A000012(n), A000045(n+1), A001333(n), A003688(n), A015448(n), A015449(n), A015451(n), A015453(n), A015454(n), A015455(n), A015456(n), A015457(n) for x = -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 respectively. - Philippe Deléham, Dec 17 2011
Sum_{k=0..n} T(n,k)*x^(n-k) = A152163(n), A000007(n), A000045(n+1), A026597(n), A122994(n+1), A158608(n), A122995(n+1), A158797(n), A122996(n+1), A158798(n), A158609(n) for x = -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 respectively. - Philippe Deléham, Dec 17 2011
G.f.: (1+(1-y)*x)/(1-y*x-x^2). - Philippe Deléham, Dec 17 2011
T(n,k) = T(n-1,k-1) + T(n-2,k), T(0,0) = T(1,0) = T(2,0) = T(2,1) = 1, T(1,1) = T(2,2) = 0, T(n,k) = 0 if k<0 or if k>n. - Philippe Deléham, Nov 09 2013

A213211 Triangular array read by rows: T(n,k) is the number of size k subsets of {1,2,...,n} such that (when the elements are arranged in increasing order) the smallest element is congruent to 1 mod 3 and the difference of every pair of successive elements is also congruent to 1 mod 3.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 3, 1, 1, 1, 1, 2, 3, 4, 1, 1, 1, 1, 3, 3, 4, 5, 1, 1, 1, 1, 3, 6, 4, 5, 6, 1, 1, 1, 1, 3, 6, 10, 5, 6, 7, 1, 1, 1, 1, 4, 6, 10, 15, 6, 7, 8, 1, 1, 1, 1, 4, 10, 10, 15, 21, 7, 8, 9, 1, 1, 1, 1, 4, 10, 20, 15, 21, 28, 8, 9, 10, 1, 1, 1
Offset: 0

Views

Author

Geoffrey Critzer, Mar 02 2013

Keywords

Comments

Row sums are A000930.

Examples

			T(6,3) = 4 because we have: {1,2,3}, {1,2,6}, {1,5,6}, {4,5,6}.
1;
1, 1;
1, 1, 1;
1, 1, 1,  1;
1, 2, 1,  1,  1;
1, 2, 3,  1,  1, 1;
1, 2, 3,  4,  1, 1, 1;
1, 3, 3,  4,  5, 1, 1, 1;
1, 3, 6,  4,  5, 6, 1, 1, 1;
1, 3, 6, 10,  5, 6, 7, 1, 1, 1;
1, 4, 6, 10, 15, 6, 7, 8, 1, 1, 1;
		

References

  • Combinatorial Enumeration, I. Goulden and D. Jackson, John Wiley and Sons, 1983, page 56.

Crossrefs

Cf. A046854.

Programs

  • Maple
    T:= (n, k)-> binomial(k+floor((n-k)/3), k):
    seq(seq(T(n,k), k=0..n), n=0..14);  # Alois P. Heinz, Mar 02 2013
  • Mathematica
    nn=10;f[list_]:=Select[list,#>0&];Map[f,CoefficientList[Series[ (1+x+x^2)/(1-x^3-y x),{x,0,nn}],{x,y}]]//Grid

Formula

G.f.: (1 + x + x^2)/(1 - x^3 - y*x).
T(n,k) = C(k+floor((n-k)/3),k). - Alois P. Heinz, Mar 02 2013

A274742 Triangle read by rows: T(n,k) (n>=3, 0<=k<=n-3) = number of n-sequences of 0's and 1's that begin with 1 and have exactly one pair of adjacent 0's and exactly k pairs of adjacent 1's.

Original entry on oeis.org

1, 1, 1, 2, 2, 1, 2, 4, 3, 1, 3, 6, 6, 4, 1, 3, 9, 12, 8, 5, 1, 4, 12, 18, 20, 10, 6, 1, 4, 16, 30, 30, 30, 12, 7, 1, 5, 20, 40, 60, 45, 42, 14, 8, 1, 5, 25, 60, 80, 105, 63, 56, 16, 9, 1, 6, 30, 75, 140, 140, 168, 84, 72, 18, 10, 1, 6, 36, 105, 175, 280, 224, 252, 108, 90, 20, 11, 1, 7, 42, 126, 280, 350, 504, 336, 360, 135, 110, 22, 12, 1
Offset: 3

Views

Author

Jeremy Dover, Jul 04 2016

Keywords

Comments

It appears that the row sums give the positive integers of A001629. - Omar E. Pol, Jul 09 2016

Examples

			n=3 => 100 -> T(3,0) = 1.
n=4 => 1001 -> T(4,0) = 1; 1100 -> T(4,1) = 1.
n=5 => 10010, 10100 -> T(5,0) = 1; 10011, 11001 -> T(5,1) = 2;
       11100 -> T(5,2) = 1.
Triangle starts:
1
1, 1
2, 2, 1
2, 4, 3, 1
3, 6, 6, 4, 1
3, 9, 12, 8, 5, 1
4, 12, 18, 20, 10, 6, 1
4, 16, 30, 30, 30, 12, 7, 1
5, 20, 40, 60, 45, 42, 14, 8, 1
5, 25, 60, 80, 105, 63, 56, 16, 9, 1
6, 30, 75, 140, 140, 168, 84, 72, 18, 10, 1
6, 36, 105, 175, 280, 224, 252, 108, 90, 20, 11, 1
7, 42, 126, 280, 350, 504, 336, 360, 135, 110, 22, 12, 1
		

Crossrefs

Columns: A008619, A087811.

Programs

  • Mathematica
    Table[Binomial[Floor[(n + k - 2)/2], k] Floor[(n - k - 1)/2], {n, 3, 15}, {k, 0, n - 3}] // Flatten (* Michael De Vlieger, Jul 05 2016 *)
  • PARI
    t(n, k) = binomial(floor((n+k-2)/2), k) * floor((n-k-1)/2)
    trianglerows(n) = for(x=3, n+2, for(y=0, x-3, print1(t(x, y), ", ")); print(""))
    trianglerows(13) \\ Felix Fröhlich, Jul 05 2016

Formula

T(n,k) = binomial(floor((n+k-2)/2),k)*floor((n-k-1)/2).

A322596 Square array read by descending antidiagonals (n >= 0, k >= 0): let b(n,k) = (n+k)!/((n+1)!*k!); then T(n,k) = b(n,k) if b(n,k) is an integer, and T(n,k) = floor(b(n,k)) + 1 otherwise.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 1, 3, 4, 3, 1, 1, 1, 3, 5, 5, 3, 1, 1, 1, 4, 7, 9, 7, 4, 1, 1, 1, 4, 10, 14, 14, 10, 4, 1, 1, 1, 5, 12, 21, 26, 21, 12, 5, 1, 1, 1, 5, 15, 30, 42, 42, 30, 15, 5, 1, 1, 1, 6, 19, 42, 66, 77, 66, 42, 19, 6, 1, 1, 1, 6, 22, 55, 99, 132, 132, 99, 55, 22, 6, 1, 1
Offset: 0

Views

Author

Keywords

Comments

For n >= 1, T(n,k) is the number of nodes in n-dimensional space for Mysovskikh's cubature formula which is exact for any polynomial of degree k of n variables.

Examples

			Array begins:
  1, 1, 1,  1,  1,   1,   1,    1,    1,    1, ...
  1, 1, 2,  2,  3,   3,   4,    4,    5,    5, ...
  1, 1, 2,  4,  5,   7,  10,   12,   15,   19, ...
  1, 1, 3,  5,  9,  14,  21,   30,   42,   55, ...
  1, 1, 3,  7, 14,  26,  42,   66,   99,  143, ...
  1, 1, 4, 10, 21,  42,  77,  132,  215,  334, ...
  1, 1, 4, 12, 30,  66, 132,  246,  429,  715, ...
  1, 1, 5, 15, 42,  99, 215,  429,  805, 1430, ...
  1, 1, 5, 19, 55, 143, 334,  715, 1430, 2702, ...
  1, 1, 6, 22, 72, 201, 501, 1144, 2431, 4862, ...
  ...
As triangular array, this begins:
  1;
  1, 1;
  1, 1,  1;
  1, 2,  1,  1;
  1, 2,  2,  1,  1;
  1, 3,  4,  3,  1,  1;
  1, 3,  5,  5,  3,  1,  1;
  1, 4,  7,  9,  7,  4,  1,  1;
  1, 4, 10, 14, 14, 10,  4,  1, 1;
  1, 5, 12, 21, 26, 21, 12,  5, 1, 1;
  1, 5, 15, 30, 42, 42, 30, 15, 5, 1, 1;
  ...
		

Crossrefs

Programs

  • Maxima
    b(n, k) := (n + k)!/((n + 1)!*k!)$
    T(n, k) := if integerp(b(n, k)) then b(n, k) else floor(b(n, k)) + 1$
    create_list(T(k, n - k), n, 0, 15, k, 0, n);

A091650 Let M = the 4 X 4 matrix [0 1 0 0 / 0 0 1 0 / 0 0 0 1 / -1 -1 3 2]. Set seed vector = [1 1 1 1] = first row, then take M*[1 1 1 1] = [1 1 1 3] then M * [1 1 1 3], etc. Sequence gives terms in rightmost column.

Original entry on oeis.org

1, 3, 7, 21, 59, 171, 491, 1415, 4073, 11729, 33771, 97241, 279993, 806209, 2321385, 6684163, 19246279, 55417453, 159568195, 459458307, 1322957467, 3809304207, 10968454313, 31582405473, 90937912211, 261845282321, 753953441489, 2170922412257, 6250921954449
Offset: 1

Views

Author

Gary W. Adamson, Jan 25 2004

Keywords

Comments

a(n)/a(n-1) tends to a 9-Gon diagonal.
The other 3 columns are offsets of 1, 3, 7, 21, 59, ... starting with 1's.
The characteristic equation of the 4 X 4 matrix is x^4 - 2x^3 - 3x^4 + x + 1 (coefficients may be found in A066170) with roots 2.879385241..., -1, -.5320888862... and .65270364466... An alternative matrix giving the same eigenvalues (refer to A046854) relates to the 9-Gon: [1 1 1 1 / 1 1 1 0 / 1 1 0 0 / 1 0 0 0] since the eigenvalue 2.8793852...is the longest diagonal of the 9-Gon given edge = 1. Or, 2.879385... = 1/(2*cos(k*Pi/9)), k = 4.

Examples

			a(5) = 59 since M*[1 1 1 1] then 4 iterates = [3 7 21 59]. a(5) = rightmost term.
a(10)/a(9) = 11729/4073 = 2.8796955...
		

Crossrefs

Programs

  • Mathematica
    Rest[CoefficientList[Series[x (1+x-2x^2-x^3)/(1-2x-3x^2+x^3+x^4),{x,0,40}],x]] (* or *) LinearRecurrence[{2,3,-1,-1},{1,3,7,21},40] (* Harvey P. Dale, Feb 17 2012 *)
  • PARI
    Vec((1+x-2*x^2-x^3)/(1-2*x-3*x^2+x^3+x^4)+O(x^99)) \\ Charles R Greathouse IV, Jan 31 2012

Formula

G.f.: x*(1+x-2*x^2-x^3)/(1-2*x-3*x^2+x^3+x^4). - Colin Barker, Jan 31 2012
a(1)=1, a(2)=3, a(3)=7, a(4)=21, a(n)=2*a(n-1)+3*a(n-2)-a(n-3)-a(n-4). - Harvey P. Dale, Feb 17 2012

Extensions

More terms from Harvey P. Dale, Feb 17 2012

A306210 T(n,k) = binomial(n + k, n) - binomial(n + floor(k/2), n) + 1, square array read by descending antidiagonals (n >= 0, k >= 0).

Original entry on oeis.org

1, 1, 1, 1, 2, 1, 1, 2, 3, 1, 1, 3, 4, 4, 1, 1, 3, 8, 7, 5, 1, 1, 4, 10, 17, 11, 6, 1, 1, 4, 16, 26, 31, 16, 7, 1, 1, 5, 19, 47, 56, 51, 22, 8, 1, 1, 5, 27, 65, 112, 106, 78, 29, 9, 1, 1, 6, 31, 101, 176, 232, 183, 113, 37, 10, 1, 1, 6, 41, 131, 296, 407, 435, 295, 157, 46, 11, 1
Offset: 0

Views

Author

Keywords

Comments

There are at most T(n,k) possible values for the number of knots in an interpolatory cubature formula of degree k for an integral over an n-dimensional region.

Examples

			Square array begins:
  1, 1,  1,   1,   1,    1,    1,    1,     1,  ...
  1, 2,  2,   3,   3,    4,    4,    5,     5,  ...
  1, 3,  4,   8,  10,   16,   19,   27,    31,  ...
  1, 4,  7,  17,  26,   47,   65,  101,   131,  ...
  1, 5, 11,  31,  56,  112,  176,  296,   426,  ...
  1, 6, 16,  51, 106,  232,  407,  737,  1162,  ...
  1, 7, 22,  78, 183,  435,  841, 1633,  2794,  ...
  1, 8, 29, 113, 295,  757, 1597, 3313,  6106,  ...
  1, 9, 37, 157, 451, 1243, 2839, 6271, 12376,  ...
  ...
As triangular array, this begins:
  1;
  1, 1;
  1, 2,  1;
  1, 2,  3,  1;
  1, 3,  4,  4,  1;
  1, 3,  8,  7,  5,  1;
  1, 4, 10, 17, 11,  6,  1;
  1, 4, 16, 26, 31, 16,  7, 1;
  1, 5, 19, 47, 56, 51, 22, 8, 1;
  ...
		

Crossrefs

Programs

  • Mathematica
    T[n_, k_] = Binomial[n + k, n] - Binomial[n + Floor[k/2], n] + 1;
    Table[T[k, n - k], {k, 0, n}, {n, 0, 20}] // Flatten
  • Maxima
    T(n, k) := binomial(n + k, n) - binomial(n + floor(k/2), n) + 1$
    create_list(T(k, n - k), n, 0, 20, k, 0, n);

Formula

T(n,k) = A007318(n+k,n) - A046854(n+k,n) + 1.
G.f.: (1 - x - x^2 + x^3 - 2*y + 2*x*y + y^2 - x*y^2 + x^2*y^2)/((1 - x)*(1 - y)*(1 - x - y)*(1 - x^2 - y)).
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