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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A171476 a(n) = 6*a(n-1) - 8*a(n-2) for n > 1, a(0)=1, a(1)=6.

Original entry on oeis.org

1, 6, 28, 120, 496, 2016, 8128, 32640, 130816, 523776, 2096128, 8386560, 33550336, 134209536, 536854528, 2147450880, 8589869056, 34359607296, 137438691328, 549755289600, 2199022206976, 8796090925056, 35184367894528
Offset: 0

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Author

Klaus Brockhaus, Dec 09 2009

Keywords

Comments

Binomial transform of A048473; second binomial transform of A151821; third binomial transform of A010684; fourth binomial transform of A084633 without second term 0; fifth binomial transform of A168589.
Inverse binomial transform of A081625; second inverse binomial transform of A081626; third inverse binomial transform of A081627.
Partial sums of A010036.
Essentially first differences of A006095.
a(n) = A109241(n) converted from binary to decimal. - Robert Price, Jan 19 2016
a(n) is the area enclosed by a Hilbert curve with unit length segments after n iterations, when the start and end points are joined. - Jennifer Buckley, Apr 23 2024

Crossrefs

Cf. A006516 (2^(n-1)*(2^n-1)), A020522 (4^n-2^n), A048473 (2*3^n-1), A151821 (powers of 2, omitting 2 itself), A010684 (repeat 1, 3), A084633 (inverse binomial transform of repeated odd numbers), A168589 ((2-3^n)*(-1)^n), A081625 (2*5^n-3^n), A081626 (2*6^n-4^n), A081627 (2*7^n-5^n), A010036 (sum of 2^n, ..., 2^(n+1)-1), A006095 (Gaussian binomial coefficient [n, 2] for q=2), A171472, A171473.

Programs

  • Magma
    [2*4^n-2^n: n in [0..30]]; // Vincenzo Librandi, Jul 17 2011
  • Mathematica
    LinearRecurrence[{6,-8},{1,6},30] (* Harvey P. Dale, Aug 02 2020 *)
  • PARI
    m=23; v=concat([1, 6], vector(m-2)); for(n=3, m, v[n]=6*v[n-1]-8*v[n-2]); v
    

Formula

a(n) = Sum_{k=1..2^n-1} k.
a(n) = 2*4^n - 2^n.
G.f.: 1/((1-2*x)*(1-4*x)).
a(n) = A006516(n+1).
a(n) = 4*a(n-1) + 2^n for n > 0, a(0)=1. - Vincenzo Librandi, Jul 17 2011
a(n) = Sum_{k=0..n} 2^(n+k). - Bruno Berselli, Aug 07 2013
a(n) = A020522(n+1)/2. - Hussam al-Homsi, Jun 06 2021
E.g.f.: exp(2*x)*(2*exp(2*x) - 1). - Stefano Spezia, Dec 10 2021

A060486 Tricoverings of an n-set.

Original entry on oeis.org

1, 0, 0, 5, 205, 11301, 904580, 101173251, 15207243828, 2975725761202, 738628553556470, 227636079973503479, 85554823285296622543, 38621481302086460057613, 20669385794052533823555309, 12966707189875262685801947906, 9441485712482676603570079314728
Offset: 0

Views

Author

Vladeta Jovovic, Mar 20 2001

Keywords

Comments

A covering of a set is a tricovering if every element of the set is covered by exactly three blocks of the covering.

Examples

			There are 1 4-block tricovering, 3 5-block tricoverings and 1 6-block tricovering of a 3-set (cf. A060487), so a(3)=5.
		

Crossrefs

Formula

E.g.f. for k-block tricoverings of an n-set is exp(-x+x^2/2+(exp(y)-1)*x^3/3)*Sum_{k=0..inf}x^k/k!*exp(-1/2*x^2*exp(k*y))*exp(binomial(k, 3)*y).

Extensions

Terms a(11) and beyond from Andrew Howroyd, Dec 15 2018

A134057 a(n) = binomial(2^n-1,2).

Original entry on oeis.org

0, 0, 3, 21, 105, 465, 1953, 8001, 32385, 130305, 522753, 2094081, 8382465, 33542145, 134193153, 536821761, 2147385345, 8589737985, 34359345153, 137438167041, 549754241025, 2199020109825, 8796086730753, 35184359505921
Offset: 0

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Author

Ross La Haye, Jan 11 2008, Jun 01 2008

Keywords

Comments

Let P(A) be the power set of an n-element set A. Then a(n) = the number of pairs of elements {x,y} of P(A) for which either 0) x and y are disjoint and for which x is not a subset of y and y is not a subset of x, or 1) x and y are intersecting but for which x is not a subset of y and y is not a subset of x, or 2) x and y are intersecting and for which either x is a proper subset of y or y is a proper subset of x.
Or: Number of connections between the nodes of the perfect depth n binary tree and the nodes of a perfect depth (n-1) binary tree. - Alex Ratushnyak, Jun 02 2013
a(n) is the number of positive entries in the positive rows and columns of a Walsh matrix of order 2^n. It is also the size of the smallest nontrivial conjugacy class in the general linear group GL(n,2). See the link "3-bit Walsh permutation...". - Tilman Piesk, Sep 15 2022

Examples

			a(2) = 3 because for P(A) = {{},{1},{2},{1,2}} we have for case 0 {{1},{2}} and we have for case 2 {{1},{1,2}}, {{2},{1,2}}. There are 0 {x,y} of P(A) in this example that fall under case 1.
		

Crossrefs

Programs

  • Magma
    [Binomial(2^n-1, 2): n in [0..30]]; // Vincenzo Librandi, Nov 30 2015
  • Maple
    seq((2^n-1)*(2^(n-1)-1), n=0..100); # Robert Israel, Nov 30 2015
  • Mathematica
    Table[Binomial[2^n - 1, 2], {n, 0, 30}] (* Vincenzo Librandi, Nov 30 2015 *)
  • PARI
    a(n) = binomial(2^n-1, 2); \\ Michel Marcus, Nov 30 2015
    
  • Python
    print([(2**n-1)*(2**(n-1)-1) for n in range(23)])
    # Alex Ratushnyak, Jun 02 2013
    

Formula

a(n) = (1/2)*(4^n - 3*2^n + 2) = 3*(Stirling2(n+1,4) + Stirling2(n+1,3)).
a(n) = 3 *A006095(n).
a(n) = (2^n-1)*(2^(n-1)-1). - Alex Ratushnyak, Jun 02 2013
a(n) = Stirling2(2^n - 1,2^n - 2).
G.f.: 3*x^2/(1-x)/(1-2*x)/(1-4*x). - Colin Barker, Feb 22 2012
a(n) = A000225(n)*A000225(n-1). - Michel Marcus, Nov 30 2015
a(n) = A000217(2^n-2). - Michel Marcus, Nov 30 2015
a(n) = 7*a(n-1) - 14*a(n-2) + 8*a(n-3). - Wesley Ivan Hurt, May 17 2021
E.g.f.: exp(x)*(exp(x) - 1)^2*(exp(x) + 2)/2. - Stefano Spezia, Apr 06 2022

A340030 Triangle read by rows: T(n,k) is the number of hypergraphs on n labeled vertices with k edges and all vertices having even degree, 0 <= k < 2^n.

Original entry on oeis.org

1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 7, 7, 0, 0, 1, 1, 0, 0, 35, 105, 168, 280, 435, 435, 280, 168, 105, 35, 0, 0, 1, 1, 0, 0, 155, 1085, 5208, 22568, 82615, 247845, 628680, 1383096, 2648919, 4414865, 6440560, 8280720, 9398115, 9398115, 8280720, 6440560, 4414865, 2648919, 1383096, 628680, 247845, 82615, 22568, 5208, 1085, 155, 0, 0, 1
Offset: 0

Views

Author

Andrew Howroyd, Jan 09 2021

Keywords

Comments

Hypergraphs are graphs in which an edge is connected to a nonempty subset of vertices rather than exactly two of them. An edge is a nonempty subset of vertices.
Equivalently, T(n,k) is the number of subsets of {1..2^n-1} with k elements such that the bitwise-xor of the elements is zero.
Also the coefficients of polynomials p_{n}(x) which have the representation
p_{n}(x) = (x + 1)^(2*(n - 1) - 1)*q_{n - 1}(x), where q_{n}(x) are the polynomials defined in A340263, and n >= 2. - Peter Luschny, Jan 10 2021

Examples

			Triangle begins:
[0]  1;
[1]  1, 0;
[2]  1, 0, 0,  1;
[3]  1, 0, 0,  7,   7,   0,   0,   1;
[4]  1, 0, 0, 35, 105, 168, 280, 435, 435, 280, 168, 105, 35, 0, 0, 1;
		

Crossrefs

Row sums are A016031(n+1).
Column k=3 gives A006095.

Programs

  • PARI
    T(n,k) = {(binomial(2^n-1, k) + (-1)^((k+1)\2)*(2^n-1)*binomial(2^(n-1)-1, k\2))/2^n}
    { for(n=0, 5, print(vector(2^n, k, T(n,k-1)))) }

Formula

T(n,k) = (binomial(2^n-1, k) + (-1)^ceiling(k/2)*(2^n-1)*binomial(2^(n-1)-1, floor(k/2)))/2^n.
T(n,2*k) + T(n,2*k+1) = binomial(2^n-1, k)/2^n = A281123(n,k).
T(n, k) = T(n, 2^n-1-k) for n >= 2.

A006118 Sum of Gaussian binomial coefficients [ n,k ] for q=4.

Original entry on oeis.org

1, 2, 7, 44, 529, 12278, 565723, 51409856, 9371059621, 3387887032202, 2463333456292207, 3557380311703796564, 10339081666350180289849, 59703612489554311631068958
Offset: 0

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Author

Keywords

References

  • J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.
  • I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p. 99.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.

Crossrefs

Row sums of triangle A022168.

Programs

  • Magma
    [n le 2 select n else 2*Self(n-1)+(4^(n-2)-1)*Self(n-2): n in [1..40]]; // Vincenzo Librandi, Aug 13 2016
  • Mathematica
    Flatten[{1,RecurrenceTable[{a[n]==2*a[n-1]+(4^(n-1)-1)*a[n-2],a[0]==1,a[1]==2},a,{n,1,15}]}] (* Vaclav Kotesovec, Aug 21 2013 *)
    Table[Sum[QBinomial[n, k, 4], {k, 0, n}], {n, 0, 20}] (* Vincenzo Librandi, Aug 13 2016 *)

Formula

a(n) = 2*a(n-1)+(4^(n-1)-1)*a(n-2), n>1. [Hitzemann and Hochstattler]. - R. J. Mathar, Aug 21 2013
a(n) ~ c * 4^(n^2/4), where c = EllipticTheta[3,0,1/4]/QPochhammer[1/4,1/4] = 2.189888057761... if n is even and c = EllipticTheta[2,0,1/4]/QPochhammer[1/4,1/4] = 2.182810929357... if n is odd. - Vaclav Kotesovec, Aug 21 2013

A006119 Sum of Gaussian binomial coefficients [ n,k ] for q=5.

Original entry on oeis.org

1, 2, 8, 64, 1120, 42176, 3583232, 666124288, 281268665344, 260766671206400, 549874114073747456, 2547649010961476288512, 26854416724405008878829568
Offset: 0

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Author

Keywords

References

  • J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.
  • I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p. 99.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.

Crossrefs

Row sums of triangle A022169.

Programs

  • Magma
    [n le 2 select n else 2*Self(n-1)+(5^(n-2)-1)*Self(n-2): n in [1..30]]; // Vincenzo Librandi, Aug 13 2016
  • Mathematica
    Flatten[{1,RecurrenceTable[{a[n]==2*a[n-1]+(5^(n-1)-1)*a[n-2],a[0]==1,a[1]==2},a,{n,1,15}]}] (* Vaclav Kotesovec, Aug 21 2013 *)
    Table[Sum[QBinomial[n, k, 5], {k, 0, n}], {n, 0, 20}] (* Vincenzo Librandi, Aug 13 2016 *)

Formula

a(n) = 2*a(n-1)+(5^(n-1)-1)*a(n-2), (Goldman + Rota, 1969). - Vaclav Kotesovec, Aug 21 2013
a(n) ~ c * 5^(n^2/4), where c = EllipticTheta[3,0,1/5]/QPochhammer[1/5,1/5] = 1.845509008203... if n is even and c = EllipticTheta[2,0,1/5]/QPochhammer[1/5,1/5] = 1.829548121746... if n is odd. - Vaclav Kotesovec, Aug 21 2013

A169720 a(n) = (3*2^(n-1)-1)*(3*2^n-1).

Original entry on oeis.org

1, 10, 55, 253, 1081, 4465, 18145, 73153, 293761, 1177345, 4713985, 18865153, 75479041, 301953025, 1207885825, 4831690753, 19327057921, 77308821505, 309236465665, 1236948221953, 4947797606401, 19791199862785, 79164818325505, 316659311050753, 1266637319700481
Offset: 0

Views

Author

Alice V. Kleeva (alice27353(AT)gmail.com), Jan 19 2010

Keywords

Comments

A subsequence of the triangular numbers A000217.

Crossrefs

Programs

  • Magma
    I:=[1, 10, 55]; [n le 3 select I[n] else 7*Self(n-1)-14*Self(n-2)+8*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Dec 03 2012
  • Mathematica
    CoefficientList[Series[(1 + 3*x - x^2)/((1-x)*(1-2*x)*(1-4*x)), {x, 0, 30}], x] (* or *) LinearRecurrence[{7, -14, 8}, {1, 10, 55}, 30] (* Vincenzo Librandi, Dec 03 2012 *)
  • PARI
    a(n)=polcoeff((1+3*x-x^2)/((1-x)*(1-2*x)*(1-4*x)+x*O(x^n)),n) \\ Paul D. Hanna, Apr 29 2010
    

Formula

G.f.: (1 + 3*x - x^2)/((1-x)*(1-2*x)*(1-4*x)). - Paul D. Hanna, Apr 29 2010
a(n) = A000217(A033484(n)). - Mitch Harris, Dec 02 2012
a(n) = 7*a(n-1) - 14*a(n-2) + 8*a(n-3). - Vincenzo Librandi, Dec 03 2012
a(n) = (3*A169726(n)-1)/2. - L. Edson Jeffery, Dec 03 2012
a(n) = A006095(n+2) +3*A006095(n+1) - A006905(n). - R. J. Mathar, Dec 04 2016

A006121 Sum of Gaussian binomial coefficients [ n,k ] for q=7.

Original entry on oeis.org

1, 2, 10, 116, 3652, 285704, 61946920, 33736398032, 51083363186704, 194585754101247008, 2061787082699360148640, 54969782721182164414355264
Offset: 0

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Author

Keywords

References

  • J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.
  • I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p. 99.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.

Programs

  • Magma
    [n le 2 select n else 2*Self(n-1)+(7^(n-2)-1)*Self(n-2): n in [1..30]]; // Vincenzo Librandi, Aug 13 2016
  • Mathematica
    Flatten[{1,RecurrenceTable[{a[n]==2*a[n-1]+(7^(n-1)-1)*a[n-2],a[0]==1,a[1]==2},a,{n,1,15}]}] (* Vaclav Kotesovec, Aug 21 2013 *)
    Table[Sum[QBinomial[n, k, 7], {k, 0, n}], {n, 0, 20}] (* Vincenzo Librandi, Aug 13 2016 *)

Formula

a(n) = 2*a(n-1)+(7^(n-1)-1)*a(n-2), (Goldman + Rota, 1969). - Vaclav Kotesovec, Aug 21 2013
a(n) ~ c * 7^(n^2/4), where c = EllipticTheta[3,0,1/7]/QPochhammer[1/7,1/7] = 1.537469386940... if n is even and c = EllipticTheta[2,0,1/7]/QPochhammer[1/7,1/7] = 1.499386995418... if n is odd. - Vaclav Kotesovec, Aug 21 2013

A006122 Sum of Gaussian binomial coefficients [ n,k ] for q=8.

Original entry on oeis.org

1, 2, 11, 148, 5917, 617894, 195118127, 162366823096, 409516908802369, 2724882133766162378, 54969878431787791720019, 2925929849527072623051175132, 472193512063977840212540697627493, 201069312609841845828101079279279809006
Offset: 0

Views

Author

Keywords

Comments

Generally, a(n) ~ c * q^(n^2/4), where c = EllipticTheta[3,0,1/q]/QPochhammer[1/q,1/q] if n is even and c = EllipticTheta[2,0,1/q]/QPochhammer[1/q,1/q] if n is odd. - Vaclav Kotesovec, Aug 21 2013

References

  • J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.
  • I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p. 99.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.

Programs

  • Magma
    [n le 2 select n else 2*Self(n-1)+(8^(n-2)-1)*Self(n-2): n in [1..40]]; // Vincenzo Librandi, Aug 13 2016
  • Mathematica
    Flatten[{1,RecurrenceTable[{a[n]==2*a[n-1]+(8^(n-1)-1)*a[n-2],a[0]==1,a[1]==2},a,{n,1,15}]}] (* Vaclav Kotesovec, Aug 21 2013 *)
    Table[Sum[QBinomial[n, k, 8], {k, 0, n}], {n, 0, 20}] (* Vincenzo Librandi, Aug 13 2016 *)

Formula

a(n) = 2*a(n-1)+(8^(n-1)-1)*a(n-2), (Goldman + Rota, 1969). - Vaclav Kotesovec, Aug 21 2013
a(n) ~ c * 8^(n^2/4), where c = EllipticTheta[3,0,1/8]/QPochhammer[1/8,1/8] = 1.455061175158... if n is even and c = EllipticTheta[2,0,1/8]/QPochhammer[1/8,1/8] = 1.405381182498... if n is odd. - Vaclav Kotesovec, Aug 21 2013

A060483 Number of 5-block tricoverings of an n-set.

Original entry on oeis.org

3, 57, 717, 7845, 81333, 825237, 8300757, 83202645, 832809813, 8331237717, 83324947797, 833299785045, 8333199127893, 83332796486997, 833331185898837, 8333324743497045, 83333298973791573, 833333195894773077, 8333332783578305877, 83333331134311650645
Offset: 3

Views

Author

Vladeta Jovovic, Mar 20 2001

Keywords

Comments

A covering of a set is a tricovering if every element of the set is covered by exactly three blocks of the covering.

Crossrefs

Programs

Formula

a(n) = (1/5!)*(10^n - 15*4^n + 45*2^n - 40).
Generally, e.g.f. for k-block tricoverings of an n-set is exp(-x+x^2/2+(exp(y)-1)*x^3/3)*Sum_{k=0..inf}x^k/k!*exp(-1/2*x^2*exp(k*y))*exp(binomial(k, 3)*y).
G.f.: 3*x^3*(2*x+1) / ((x-1)*(2*x-1)*(4*x-1)*(10*x-1)). - Colin Barker, Jan 11 2013

Extensions

More terms from Colin Barker, Jan 11 2013
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