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 11-20 of 28 results. Next

A008813 Expansion of (1+x^6)/((1-x)^2*(1-x^6)).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 21, 24, 29, 34, 39, 44, 49, 54, 61, 68, 75, 82, 89, 96, 105, 114, 123, 132, 141, 150, 161, 172, 183, 194, 205, 216, 229, 242, 255, 268, 281, 294, 309, 324, 339, 354, 369, 384, 401, 418, 435, 452, 469, 486, 505, 524, 543, 562
Offset: 0

Views

Author

Keywords

Comments

Number of 0..n arrays of 7 elements with zero second differences. - R. H. Hardin, Nov 16 2011

Crossrefs

Cf. Expansions of the form (1+x^m)/((1-x)^2*(1-x^m)): A000290 (m=1), A000982 (m=2), A008810 (m=3), A008811 (m=4), A008812 (m=5), this sequence (m=6), A008814 (m=7), A008815 (m=8), A008816 (m=9), A008817 (m=10).

Programs

  • GAP
    a:=[1,2,3,4,5,6,9,12];; for n in [9..70] do a[n]:=2*a[n-1]-a[n-2] +a[n-6]-2*a[n-7]+a[n-8]; od; a; # G. C. Greubel, Sep 12 2019
  • Magma
    R:=PowerSeriesRing(Integers(), 70); Coefficients(R!( (1+x^6)/((1-x)^2*(1-x^6)) )); // G. C. Greubel, Sep 12 2019
    
  • Maple
    seq(coeff(series((1+x^6)/((1-x)^2*(1-x^6)), x, n+1), x, n), n = 0..70); # G. C. Greubel, Sep 12 2019
  • Mathematica
    CoefficientList[Series[(1+x^6)/(1-x)^2/(1-x^6), {x,0,70}], x] (* or *) LinearRecurrence[{2,-1,0,0,0,1,-2,1}, {1,2,3,4,5,6,9,12}, 70] (* Harvey P. Dale, Oct 13 2012 *)
  • PARI
    Vec((1+x^6)/((1-x)^2*(1-x^6)) +O(x^70)) \\ Charles R Greathouse IV, Sep 26 2012
    
  • Sage
    def A008813_list(prec):
        P. = PowerSeriesRing(ZZ, prec)
        return P((1+x^6)/((1-x)^2*(1-x^6))).list()
    A008813_list(70) # G. C. Greubel, Sep 12 2019
    

Formula

G.f.: (1+x^6)/((1-x)^2*(1-x^6)).
a(n) = 2*a(n-1) -a(n-2) +a(n-6) -2*a(n-7) +a(n-8). - R. H. Hardin, Nov 16 2011

Extensions

More terms added by G. C. Greubel, Sep 12 2019

A008814 Expansion of (1+x^7)/((1-x)^2*(1-x^7)).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 10, 13, 16, 19, 22, 25, 28, 33, 38, 43, 48, 53, 58, 63, 70, 77, 84, 91, 98, 105, 112, 121, 130, 139, 148, 157, 166, 175, 186, 197, 208, 219, 230, 241, 252, 265, 278, 291, 304, 317, 330, 343, 358, 373, 388, 403, 418, 433, 448, 465, 482, 499
Offset: 0

Views

Author

Keywords

Comments

Number of 0..n arrays of 8 elements with zero second differences. - R. H. Hardin, Nov 16 2011

Crossrefs

Cf. Expansions of the form (1+x^m)/((1-x)^2*(1-x^m)): A000290 (m=1), A000982 (m=2), A008810 (m=3), A008811 (m=4), A008812 (m=5), A008813 (m=6), this sequence (m=7), A008815 (m=8), A008816 (m=9), A008817 (m=10).

Programs

  • GAP
    a:=[1,2,3,4,5,6,7,10,13];; for n in [10..70] do a[n]:=2*a[n-1]-a[n-2]+a[n-7]-2*a[n-8]+a[n-9]; od; a; # G. C. Greubel, Sep 12 2019
  • Magma
    R:=PowerSeriesRing(Integers(), 70); Coefficients(R!( (1+x^7)/((1-x)^2*(1-x^7)) )); // G. C. Greubel, Sep 12 2019
    
  • Maple
    seq(coeff(series((1+x^7)/((1-x)^2*(1-x^7)), x, n+1), x, n), n = 0..70); # G. C. Greubel, Sep 12 2019
  • Mathematica
    CoefficientList[Series[(1+x^7)/(1-x)^2/(1-x^7), {x,0,70}], x] (* or *)
    LinearRecurrence[{2,-1,0,0,0,0,1,-2,1}, {1,2,3,4,5,6,7,10,13}, 70] (* Harvey P. Dale, Dec 18 2012 *)
  • PARI
    a(n)=(n*(n+2)+[7,11,13,13,11,7,1][n%7+1])/7 \\ Charles R Greathouse IV, Nov 16 2011
    
  • PARI
    a(n)=(n*(n+2)+13-6*(n%7==6))\7  \\ Tani Akinari, Jul 25 2013
    
  • Sage
    def A008814_list(prec):
        P. = PowerSeriesRing(ZZ, prec)
        return P((1+x^7)/((1-x)^2*(1-x^7))).list()
    A008814_list(70) # G. C. Greubel, Sep 12 2019
    

Formula

G.f.: (1+x^7)/((1-x)^2*(1-x^7)).
a(n) = 2*a(n-1) -a(n-2) +a(n-7) -2*a(n-8) +a(n-9). - R. H. Hardin, Nov 16 2011

Extensions

More terms added by G. C. Greubel, Sep 12 2019

A008815 Expansion of (1+x^8)/((1-x)^2*(1-x^8)).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 11, 14, 17, 20, 23, 26, 29, 32, 37, 42, 47, 52, 57, 62, 67, 72, 79, 86, 93, 100, 107, 114, 121, 128, 137, 146, 155, 164, 173, 182, 191, 200, 211, 222, 233, 244, 255, 266, 277, 288, 301, 314, 327, 340, 353, 366, 379, 392, 407, 422
Offset: 0

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Author

Keywords

Crossrefs

Cf. Expansions of the form (1+x^m)/((1-x)^2*(1-x^m)): A000290 (m=1), A000982 (m=2), A008810 (m=3), A008811 (m=4), A008812 (m=5), A008813 (m=6), A008814 (m=7), this sequence (m=8), A008816 (m=9), A008817 (m=10).

Programs

  • GAP
    a:=[1,2,3,4,5,6,7,8,11,14];; for n in [11..50] do a[n]:=2*a[n-1] -a[n-2]+a[n-8]-2*a[n-9]+a[n-10]; od; a; # G. C. Greubel, Sep 12 2019
  • Magma
    I:=[1,2,3,4,5,6,7,8,11,14]; [n le 10 select I[n] else 2*Self(n-1) -Self(n-2)+Self(n-8)-2*Self(n-9)+Self(n-10): n in [1..50]]; // Vincenzo Librandi, May 14 2019
    
  • Maple
    seq(coeff(series((1+x^8)/((1-x)^2*(1-x^8)), x, n+1), x, n), n = 0..50); # G. C. Greubel, Sep 12 2019
  • Mathematica
    CoefficientList[Series[(1+x^8)/(1-x)^2/(1-x^8), {x, 0, 50}], x] (* or *) LinearRecurrence[{2,-1,0,0,0,0,0,1,-2,1}, {1,2,3,4,5,6,7,8,11,14}, 50] (* Harvey P. Dale, Dec 17 2016 *)
  • PARI
    a(n)=(n*(n+2)+14+4*(n%4-1)*(-1)^(n\4))\8  \\ Tani Akinari, Jul 25 2013
    
  • Sage
    def A008815_list(prec):
        P. = PowerSeriesRing(ZZ, prec)
        return P((1+x^8)/((1-x)^2*(1-x^8))).list()
    A008815_list(50) # G. C. Greubel, Sep 12 2019
    

Formula

G.f.: (1 + x^8)/((1 - x)^3*(1 + x)*(1 + x^2)*(1 + x^4)).
a(n) = floor( (n*(n+2) + 14 + 4*((n mod 4) - 1)*(-1)^floor(n/4))/8 ). - Tani Akinari, Jul 25 2013
a(n) = 2*a(n-1) - a(n-2) + a(n-8) - 2*a(n-9) + a(n-10). - Vincenzo Librandi, May 14 2019

A200082 T(n,k)=Number of 0..k arrays x(0..n) of n+1 elements with zero n-1st differences.

Original entry on oeis.org

1, 1, 2, 1, 3, 2, 1, 4, 3, 2, 1, 5, 6, 3, 2, 1, 6, 9, 8, 7, 2, 1, 7, 12, 17, 14, 9, 2, 1, 8, 17, 26, 27, 18, 9, 2, 1, 9, 22, 43, 58, 37, 24, 15, 2, 1, 10, 27, 64, 111, 108, 85, 56, 7, 2, 1, 11, 34, 89, 182, 245, 202, 169, 26, 3, 2, 1, 12, 41, 122, 279, 454, 429, 394, 151, 26, 11, 2, 1, 13, 48
Offset: 1

Views

Author

R. H. Hardin Nov 13 2011

Keywords

Comments

Table starts
.1..1..1...1...1....1.....1.....1.....1......1......1......1.......1.......1
.2..3..4...5...6....7.....8.....9....10.....11.....12.....13......14......15
.2..3..6...9..12...17....22....27....34.....41.....48.....57......66......75
.2..3..8..17..26...43....64....89...122....163....208....269.....334.....407
.2..7.14..27..58..111...182...279...404....617....872...1199....1580....2045
.2..9.18..37.108..245...454...759..1172...2001...3144...4663....6568....8945
.2..9.24..85.202..429..1046..2145..4022...6955..11438..17927...26868...41817
.2.15.56.169.394..855..2546..6179.12710..23899..41522..68427..106948..183797
.2..7.26.151.468.1863..5056.12965.29904..64603.124728.243309..432190..748301
.2..3.26.219.848.3573.11638.31507.84560.198435.418330.878657.1704398.3107463
T(n,k) is the number of integer lattice points in k*C(n) where C(n) is the polytope in R^(n+1) defined by two linear equations and the bounds 0 <= x_i <= 1. Since the vertices of this polytope have rational coordinates, T(n,k) for each fixed n is an Ehrhart quasi-polynomial of degree n-1. - Robert Israel, Nov 11 2019

Examples

			Some solutions for n=7 k=6
..1....4....5....4....5....0....2....6....0....4....6....1....2....3....1....4
..5....2....3....5....0....1....1....1....4....5....4....3....0....6....0....0
..2....6....4....4....5....3....2....3....6....3....0....5....2....3....4....2
..1....6....3....3....5....3....3....5....6....2....0....4....4....0....6....3
..3....3....1....3....1....2....3....5....5....3....2....2....4....0....5....2
..5....2....1....4....0....2....2....4....4....5....2....2....2....3....3....1
..4....5....4....5....5....3....1....4....3....6....0....4....0....6....2....2
..1....4....5....4....5....0....2....6....0....4....6....1....2....3....1....4
		

Crossrefs

Row 3 is A008810(n+1)

A008816 Expansion of (1+x^9)/((1-x)^2*(1-x^9)).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 41, 46, 51, 56, 61, 66, 71, 76, 81, 88, 95, 102, 109, 116, 123, 130, 137, 144, 153, 162, 171, 180, 189, 198, 207, 216, 225, 236, 247, 258, 269, 280, 291, 302, 313, 324, 337, 350, 363, 376, 389, 402
Offset: 0

Views

Author

Keywords

Crossrefs

Cf. Expansions of the form (1+x^m)/((1-x)^2*(1-x^m)): A000290 (m=1), A000982 (m=2), A008810 (m=3), A008811 (m=4), A008812 (m=5), A008813 (m=6), A008814 (m=7), A008815 (m=8), this sequence (m=9), A008817 (m=10).

Programs

  • GAP
    a:=[1,2,3,4,5,6,7,8,9,12,15];; for n in [12..70] do a[n]:=2*a[n-1] -a[n-2]+a[n-9]-2*a[n-10]+a[n-11]; od; a; # G. C. Greubel, Sep 12 2019
  • Magma
    R:=PowerSeriesRing(Integers(), 70); Coefficients(R!( (1+x^9)/((1-x)^2*(1-x^9)) )); // G. C. Greubel, Sep 12 2019
    
  • Maple
    seq(coeff(series((1+x^9)/((1-x)^2*(1-x^9)), x, n+1), x, n), n = 0..50); # G. C. Greubel, Sep 12 2019
  • Mathematica
    LinearRecurrence[{2,-1,0,0,0,0,0,0,1,-2,1}, {1,2,3,4,5,6,7,8,9,12,15}, 70] (* or *) CoefficientList[Series[(1+x^9)/((1-x)^2*(1-x^9)), {x,0, 70}], x] (* G. C. Greubel, Sep 12 2019 *)
  • PARI
    my(x='x+O('x^70)); Vec((1+x^9)/((1-x)^2*(1-x^9))) \\ G. C. Greubel, Sep 12 2019
    
  • Sage
    def A008815_list(prec):
        P. = PowerSeriesRing(ZZ, prec)
        return P((1+x^8)/((1-x)^2*(1-x^8))).list()
    A008815_list(70) # G. C. Greubel, Sep 12 2019
    

Formula

G.f.: (1+x^9)/((1-x)^2*(1-x^9)). - G. C. Greubel, Sep 12 2019

Extensions

More terms added by G. C. Greubel, Sep 12 2019

A008817 Expansion of (1+x^10)/((1-x)^2*(1-x^10)).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 16, 19, 22, 25, 28, 31, 34, 37, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 97, 104, 111, 118, 125, 132, 139, 146, 153, 160, 169, 178, 187, 196, 205, 214, 223, 232, 241, 250, 261, 272, 283, 294, 305, 316, 327, 338, 349, 360
Offset: 0

Views

Author

Keywords

Crossrefs

Cf. Expansions of the form (1+x^m)/((1-x)^2*(1-x^m)): A000290 (m=1), A000982 (m=2), A008810 (m=3), A008811 (m=4), A008812 (m=5), A008813 (m=6), A008814 (m=7), A008815 (m=8), A008816 (m=9), this sequence (m=10).

Programs

  • GAP
    a:=[1,2,3,4,5,6,7,8,9,10, 13,16];; for n in [13..80] do a[n]:=2*a[n-1]-a[n-2]+a[n-10]-2*a[n-11]+a[n-12]; od; a; # G. C. Greubel, Sep 12 2019
  • Magma
    R:=PowerSeriesRing(Integers(), 80); Coefficients(R!( (1+x^10)/((1-x)^2*(1-x^10)) )); // G. C. Greubel, Sep 12 2019
    
  • Maple
    seq(coeff(series((1+x^10)/((1-x)^2*(1-x^10)), x, n+1), x, n), n = 0..80); # G. C. Greubel, Sep 12 2019
  • Mathematica
    CoefficientList[Series[(1+x^10)/(1-x)^2/(1-x^10), {x,0,80}], x] (* or *) LinearRecurrence[{2,-1,0,0,0,0,0,0,0,1,-2,1}, {1,2,3,4,5,6,7,8,9,10, 13,16}, 80] (* Harvey P. Dale, Jul 31 2014 *)
  • PARI
    my(x='x+O('x^80)); Vec((1+x^10)/((1-x)^2*(1-x^10))) \\ G. C. Greubel, Sep 12 2019
    
  • Sage
    def A008817_list(prec):
        P. = PowerSeriesRing(ZZ, prec)
        return P((1+x^10)/((1-x)^2*(1-x^10))).list()
    A008817_list(80) # G. C. Greubel, Sep 12 2019
    

Formula

G.f.: (1+x^10)/((1-x)^2*(1-x^10)).
a(0)=1, a(1)=2, a(2)=3, a(3)=4, a(4)=5, a(5)=6, a(6)=7, a(7)=8, a(8)=9, a(9)=10, a(10)=13, a(11)=16, a(n) = 2*a(n-1) - a(n-2) + a(n-10) - 2*a(n-11) + a(n-12). - Harvey P. Dale, Jul 31 2014

A143977 Rectangular array R by antidiagonals: label each unit square in the first quadrant lattice by its northeast vertex (x,y) and mark squares having |x-y| == 0 (mod 3); then R(m,n) is the number of marked squares in the rectangle [0,m] X [0,n].

Original entry on oeis.org

1, 1, 1, 1, 2, 1, 2, 2, 2, 2, 2, 3, 3, 3, 2, 2, 4, 4, 4, 4, 2, 3, 4, 5, 6, 5, 4, 3, 3, 5, 6, 7, 7, 6, 5, 3, 3, 6, 7, 8, 9, 8, 7, 6, 3, 4, 6, 8, 10, 10, 10, 10, 8, 6, 4, 4, 7, 9, 11, 12, 12, 12, 11, 9, 7, 4, 4, 8, 10, 12, 14, 14, 14, 14, 12, 10, 8, 4, 5, 8, 11, 14, 15, 16, 17, 16, 15, 14, 11, 8, 5
Offset: 1

Views

Author

Clark Kimberling, Sep 06 2008

Keywords

Comments

Rows numbered 3,6,9,12,15,... are, except for initial terms, multiples of (1,2,3,4,5,6,7,...) = A000027.

Examples

			Northwest corner:
  1  1  1  2  2  2  3
  1  2  2  3  4  4  5
  1  2  3  4  5  6  7
  2  3  4  6  7  8 10
  2  4  5  7  9 10 12
		

Crossrefs

Rows and columns: A002264, A004523, A000027, A004772, A047212, et al.

Programs

  • Mathematica
    T[m_,n_]:=Ceiling[m n/3];Flatten[Table[T[m-n+1,n],{m,13},{n,m}]] (* Stefano Spezia, Oct 27 2022 *)

Formula

R(m,n) = ceiling(m*n/3). [Corrected by Stefano Spezia, Oct 27 2022]

A023133 Signature sequence of Pi (arrange the numbers i+j*x (i,j >= 1) in increasing order; the sequence of i's is the signature of x).

Original entry on oeis.org

1, 2, 3, 4, 1, 5, 2, 6, 3, 7, 4, 1, 8, 5, 2, 9, 6, 3, 10, 7, 4, 1, 11, 8, 5, 2, 12, 9, 6, 3, 13, 10, 7, 4, 1, 14, 11, 8, 5, 2, 15, 12, 9, 6, 3, 16, 13, 10, 7, 4, 1, 17, 14, 11, 8, 5, 2, 18, 15, 12, 9, 6, 3, 19, 16, 13, 10, 7, 4, 1, 20, 17, 14, 11, 8, 5, 2, 21, 18, 15, 12, 9, 6, 3
Offset: 1

Views

Author

Keywords

References

  • C. Kimberling, "Fractal Sequences and Interspersions", Ars Combinatoria, vol. 45 p 157 1997.

Crossrefs

Programs

  • PARI
    lista(nn) = {v = vector(nn^2, k, kij = k+nn-1; i = 1+(kij % nn); j = kij\nn; i+j*Pi); vs = vecsort(v, , 1); for (k=1, #vs, print1(curi = 1+((vs[k]+nn-1) % nn), ", "); if (curi == nn, break));} \\ Michel Marcus, Apr 10 2015

A280984 Minimum number of dominoes on an n X n chessboard needed to prevent placement of another domino.

Original entry on oeis.org

0, 2, 3, 6, 9, 12, 17, 22, 27, 34, 41, 48, 57, 66, 75, 86, 97, 108, 122, 134, 147, 163, 178, 192, 210, 227, 243, 263, 282, 300, 322, 343, 363
Offset: 1

Views

Author

Rick L. Shepherd, Jan 11 2017, Aug 06 2017

Keywords

Comments

Each domino must cover exactly two adjacent squares of a row or column. Sequence inspired by question for 8 X 8 case in "Minimum Guard Problem" link.
A.k.a. lower matching number of the n X n grid graph. - Eric W. Weisstein, Dec 16 2024
a(n) = 0 for n = 1, a(n) = ceiling(n^2/3) + 1 for n = 19, 22, 23, 25, 26, 28, 29, 31, 32, and a(n) = ceiling(n^2/3) for other n <= 32. - Eric W. Weisstein, Dec 16 2024

Crossrefs

Cf. A008810 (maximum number of L-shaped trominoes with the same orientation in an n X n square, a.k.a. ceil(n^2/3)).
Cf. A378763 (lower matching number of the n X n torus grid graph).
Cf. A379177 (lower matching number of the n X n X n grid graph).

Formula

Proved: a(n) >= A008810(n) for n>1; when n = 0 (mod 3), a(n) = A008810(n). - Andrey Zabolotskiy, Oct 22 2017
a(n) > n^2/3 + n/111 for large n not congruent to 0 (mod 3) [from Gyárfás, Lehel, Tuza]. - Peter Kagey, May 22 2019

Extensions

a(10)-a(14) from Lars Blomberg, Aug 08 2017
a(15) from Andrey Zabolotskiy, Oct 20 2017
a(16)-a(17) from Rob Pratt (see the link to Peter Kagey's question) and a(18) added by Andrey Zabolotskiy, Feb 13 2020
a(19)-a(33) from Walter Trump, Jun 14 2020

A225215 Floor of the Euclidean distance of a point on the (1, 1, 1; 1, 1, 1) 3D walk.

Original entry on oeis.org

1, 1, 1, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 8, 8, 9, 9, 10, 11, 11, 12, 12, 13, 13, 14, 15, 15, 16, 16, 17, 17, 18, 19, 19, 20, 20, 21, 21, 22, 23, 23, 24, 24, 25, 25, 26, 27, 27, 28, 28, 29, 30, 30, 31, 31, 32, 32, 33, 34, 34, 35, 35, 36, 36, 37, 38, 38, 39, 39, 40, 41, 41, 42, 42, 43, 43, 44, 45, 45, 46, 46, 47, 47, 48, 49, 49, 50, 50
Offset: 1

Views

Author

Jon Perry, May 02 2013

Keywords

Comments

Consider a standard 3-dimensional Euclidean lattice. We take 1 step along the positive x-axis, 1 along the positive y-axis, 1 along the positive z-axis, 1 along the positive x-axis, and so on. After 3, 6, 9, 12, 15 etc steps we have returned to the space diagonal (with equal x, y and z coordinates).
This sequence gives the floor of the Euclidean distance to the origin after n steps.

Crossrefs

Programs

  • JavaScript
    p = new Array(0, 0, 0);
    for (a = 1; a < 100; a++) {
    p[a%3] += 1;
    document.write(Math.floor(Math.sqrt(p[0] * p[0] + p[1] * p[1] + p[2] * p[2])) + ", ");
    }

Formula

a(n) ~ n/sqrt(3). - Charles R Greathouse IV, May 02 2013
a(n) = floor(sqrt(A008810(n))), where A008810(n) is the squared Euclidean distance after n steps. - R. J. Mathar, May 02 2013
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