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 21-30 of 40 results. Next

A256315 Number of partitions of 3n into exactly 6 parts.

Original entry on oeis.org

0, 0, 1, 3, 11, 26, 58, 110, 199, 331, 532, 811, 1206, 1729, 2432, 3331, 4494, 5942, 7760, 9975, 12692, 15944, 19858, 24473, 29941, 36308, 43752, 52327, 62239, 73551, 86499, 101155, 117788, 136479, 157532, 181038, 207338, 236534, 269005, 304865, 344534
Offset: 0

Views

Author

Colin Barker, Mar 23 2015

Keywords

Comments

Also the number of partitions of 3*(n-2) into at most 6 parts. - Colin Barker, Apr 01 2015

Examples

			For n=3 the 3 partitions of 3*3 = 9 are [1,1,1,1,1,4], [1,1,1,1,2,3] and [1,1,1,2,2,2].
		

Crossrefs

Programs

  • Mathematica
    CoefficientList[Series[x^2*(x^8 + x^7 + 4*x^6 + 5*x^5 + 5*x^4 + 5*x^3 + 4*x^2 + x + 1)/((x - 1)^6*(x + 1)^3*(x^2 + 1)*(x^4 + x^3 + x^2 + x + 1)), {x, 0, 50}], x] (* Wesley Ivan Hurt, Feb 22 2017 *)
    Table[Length@ IntegerPartitions[3 n, {6}], {n, 0, 40}] (* Michael De Vlieger, Feb 22 2017 *)
  • PARI
    concat(0, vector(40, n, k=0; forpart(p=3*n, k++, , [6,6]); k))
    
  • PARI
    concat([0,0], Vec(x^2*(x^8+x^7+4*x^6+5*x^5+5*x^4+5*x^3+4*x^2+x+1) / ((x-1)^6*(x+1)^3*(x^2+1)*(x^4+x^3+x^2+x+1)) + O(x^100)))

Formula

G.f.: x^2*(x^8+x^7+4*x^6+5*x^5+5*x^4+5*x^3+4*x^2+x+1) / ((x-1)^6*(x+1)^3*(x^2+1)*(x^4+x^3+x^2+x+1)).

A238410 a(n) = floor((3(n-1)^2 + 1)/2).

Original entry on oeis.org

0, 2, 6, 14, 24, 38, 54, 74, 96, 122, 150, 182, 216, 254, 294, 338, 384, 434, 486, 542, 600, 662, 726, 794, 864, 938, 1014, 1094, 1176, 1262, 1350, 1442, 1536, 1634, 1734, 1838, 1944, 2054, 2166, 2282, 2400, 2522, 2646, 2774, 2904, 3038, 3174, 3314, 3456, 3602, 3750, 3902, 4056, 4214, 4374, 4538, 4704
Offset: 1

Views

Author

Emeric Deutsch, Feb 27 2014

Keywords

Comments

a(n) = the eccentric connectivity index of the path P[n] on n vertices. The eccentric connectivity index of a simple connected graph G is defined to be the sum over all vertices i of G of the product E(i)D(i), where E(i) is the eccentricity and D(i) is the degree of vertex i. For example, a(4)=14 because the vertices of P[4] have degrees 1,2,2,1 and eccentricities 3,2,2,3; we have 1*3 + 2*2 + 2*2 + 1*3 = 14.
From Paul Curtz, Feb 23 2023: (Start)
East spoke of the hexagonal spiral using A004526 with a single 0:
.
43 42 42 41 41 40
43 28 28 27 27 26 40
44 29 17 16 16 15 26 39
44 29 17 8 8 7 15 25 39
45 30 18 9 3 2 7 14 25 38
45 30 18 9 3 0---2---6--14--24--38-->
31 19 10 4 1 1 6 13 24 37
31 19 10 4 5 5 13 23 37
32 20 11 11 12 12 23 36
32 20 21 21 22 22 36
33 33 34 34 35 35
.

Crossrefs

Programs

  • Maple
    a := proc (n) options operator, arrow: floor((3/2)*(n-1)^2+1/2) end proc: seq(a(n), n = 1 .. 70);
  • Mathematica
    Table[Floor[(3(n-1)^2+1)/2],{n,80}]  (* or *) LinearRecurrence[{2,0,-2,1},{0,2,6,14},80] (* Harvey P. Dale, Apr 30 2022 *)
  • PARI
    a(n)=(3*(n-1)^2 + 1)\2 \\ Charles R Greathouse IV, Feb 15 2017

Formula

a(n) = (3*n)^2/6 for n even and a(n) = ((3*n)^2 + 3)/6 for n odd. - Miquel Cerda, Jun 17 2016
From Ilya Gutkovskiy, Jun 17 2016: (Start)
G.f.: 2*x^2*(1 + x + x^2)/((1 - x)^3*(1 + x)).
a(n) = (6*n^2 - 12*n + 7 + (-1)^n)/4.
a(n) = 2* A077043(n-1). (End)
a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4). - Matthew House, Feb 15 2017
Sum_{n>=2} 1/a(n) = Pi^2/36 + tanh(Pi/(2*sqrt(3)))*Pi/(2*sqrt(3)). - Amiram Eldar, Mar 12 2023

A256226 Number of partitions of 6n into 6 parts.

Original entry on oeis.org

0, 1, 11, 58, 199, 532, 1206, 2432, 4494, 7760, 12692, 19858, 29941, 43752, 62239, 86499, 117788, 157532, 207338, 269005, 344534, 436140, 546261, 677571, 832989, 1015691, 1229120, 1476997, 1763332, 2092435, 2468926, 2897747, 3384171, 3933815, 4552649, 5247008
Offset: 0

Views

Author

Colin Barker, Mar 19 2015

Keywords

Examples

			For n=2, the 11 partitions of 12 are Xs = [7,1,1,1,1,1], [6,2,1,1,1,1], [5,3,1,1,1,1], [4,4,1,1,1,1], [5,2,2,1,1,1], [4,3,2,1,1,1], [3,3,3,1,1,1], [4,2,2,2,1,1], [3,3,2,2,1,1], [3,2,2,2,2,1] and [2,2,2,2,2,2].
		

Crossrefs

Programs

  • Mathematica
    CoefficientList[Series[x (3 x^7 + 14 x^6 + 21 x^5 + 21 x^4 + 22 x^3 + 19 x^2 + 7 x + 1) / ((x - 1)^6 (x + 1) (x^4 + x^3 + x^2 + x + 1)), {x, 0, 40}], x] (* Vincenzo Librandi, Mar 20 2015 *)
  • PARI
    concat(0, Vec(x*(3*x^7+14*x^6+21*x^5+21*x^4+22*x^3+19*x^2+7*x+1)/((x-1)^6*(x+1)*(x^4+x^3+x^2+x+1)) + O(x^100)))
    
  • PARI
    concat(0, vector(35, n, k=0; forpart(p=6*n, k++, , [6,6]); k)) \\ Colin Barker, Mar 21 2015

Formula

G.f.: x*(3*x^7+14*x^6+21*x^5+21*x^4+22*x^3+19*x^2+7*x+1) / ((x-1)^6*(x+1)*(x^4+x^3+x^2+x+1)).

A330707 a(n) = ( 3*n^2 + n - 1 + (-1)^floor(n/2) )/4.

Original entry on oeis.org

0, 1, 3, 7, 13, 20, 28, 38, 50, 63, 77, 93, 111, 130, 150, 172, 196, 221, 247, 275, 305, 336, 368, 402, 438, 475, 513, 553, 595, 638, 682, 728, 776, 825, 875, 927, 981, 1036, 1092, 1150, 1210, 1271, 1333, 1397, 1463
Offset: 0

Views

Author

Paul Curtz, Dec 27 2019

Keywords

Comments

Essentially four odds followed by four evens.
Last digit is neither 4 nor 9.
Essentially twice or twin sequences in the hexagonal spiral from A002265.
21 21 21 22 22 22 22
21 14 14 14 14 15 15 23
20 13 8 8 8 9 9 15 23
20 13 8 4 4 4 4 9 15 23
20 13 7 3 1 1 1 5 9 16 23
20 13 7 3 1 0 0 2 5 10 16 24
19 12 7 3 0 0 2 5 10 16 24
19 12 7 3 2 2 5 10 16 24
19 12 6 6 6 6 10 17 24
19 12 11 11 11 11 17 25
18 18 18 18 17 17 25
.
There are 12 twin sequences. 6 of them (A001859, A006578, A077043, A231559, A024219, A281026) are in the OEIS. a(n) is the seventh.
0, 1, 3, 7, 13, 20, 28, 38, 50, ...
1, 2, 4, 6, 7, 8, 10, 12, 13, ...
1, 2, 2, 1, 1, 2, 2, 1, 1, ... period 4. See A014695.

Crossrefs

Programs

  • Magma
    [(3*n^2+n-1+ (-1)^Floor(n/2))/4: n in [0..60]]; // G. C. Greubel, Dec 30 2019
    
  • Maple
    seq((3*n^2+n-1+sqrt(2)*sin((2*n+1)*Pi/4))/4, n = 0..60); # G. C. Greubel, Dec 30 2019
  • Mathematica
    LinearRecurrence[{3,-4,4,-3,1}, {0,1,3,7,13}, 60] (* Amiram Eldar, Dec 27 2019 *)
  • PARI
    concat(0, Vec(x*(1 + 2*x^2) / ((1 - x)^3*(1 + x^2)) + O(x^60))) \\ Colin Barker, Dec 27 2019
    
  • Sage
    [(3*n^2+n-1+(-1)^floor(n/2))/4 for n in (0..60)] # G. C. Greubel, Dec 30 2019

Formula

a(n) = A231559(-n).
a(1+2*n) + a(2+2*n) = A033579(n+1).
a(40+n) - a(n) = 1210, 1270, 1330, 1390, 1450, ... . See 10*A016921(n).
From Colin Barker, Dec 27 2019: (Start)
G.f.: x*(1 + 2*x^2) / ((1 - x)^3*(1 + x^2)).
a(n) = 3*a(n-1) - 4*a(n-2) + 4*a(n-3) - 3*a(n-4) + a(n-5) for n>4.
(End)
E.g.f.: (cos(x) + sin(x) + (-1 + 4*x + 3*x^2)*exp(x))/4. - Stefano Spezia, Dec 27 2019
a(n) = ( 3*n^2 + n - 1 + sqrt(2)*sin((2*n+1)*Pi/4) )/4 = ( 3*n^2 + n - 1 + (-1)^floor(n/2) )/4. - G. C. Greubel, Dec 30 2019

A227568 Largest k such that a partition of n into distinct parts with boundary size k exists.

Original entry on oeis.org

0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10
Offset: 0

Views

Author

Alois P. Heinz, Jul 16 2013

Keywords

Comments

The boundary size is the number of parts having fewer than two neighbors.

Crossrefs

Where records occur: A077043.

Programs

  • Maple
    b:= proc(n, i, t) option remember; `if`(n=0, `if`(t>1, 1, 0),
          `if`(i<1, 0, max(`if`(t>1, 1, 0)+b(n, i-1, iquo(t, 2)),
          `if`(i>n, 0, `if`(t=2, 1, 0)+b(n-i, i-1, iquo(t, 2)+2)))))
        end:
    a:= n-> b(n$2, 0):
    seq(a(n), n=0..100);
  • Mathematica
    b[n_, i_, t_] := b[n, i, t] = If[n == 0, If[t > 1, 1, 0], If[i < 1, 0, Max[If[t > 1, 1, 0] + b[n, i - 1, Quotient[t, 2]], If[i > n, 0, If[t == 2, 1, 0] + b[n - i, i - 1, Quotient[t, 2] + 2]]]]];
    a[n_] := b[n, n, 0];
    Table[a[n], {n, 0, 100}] (* Jean-François Alcover, May 21 2018, translated from Maple *)

Formula

a(n) = max { k : A227345(n,k) > 0 } = max { k : A227551(n,k) > 0 }.
a(n) = floor(2*sqrt(n/3)).

A256313 Number of partitions of 3n into exactly 4 parts.

Original entry on oeis.org

0, 0, 2, 6, 15, 27, 47, 72, 108, 150, 206, 270, 351, 441, 551, 672, 816, 972, 1154, 1350, 1575, 1815, 2087, 2376, 2700, 3042, 3422, 3822, 4263, 4725, 5231, 5760, 6336, 6936, 7586, 8262, 8991, 9747, 10559, 11400, 12300, 13230, 14222, 15246, 16335, 17457
Offset: 0

Views

Author

Colin Barker, Mar 23 2015

Keywords

Examples

			For n=3 the 6 partitions of 3*3 = 9 are [1,1,1,6], [1,1,2,5], [1,1,3,4], [1,2,2,4], [1,2,3,3] and [2,2,2,3].
		

Crossrefs

Programs

  • Mathematica
    LinearRecurrence[{2,0,-2,2,-2,0,2,-1},{0,0,2,6,15,27,47,72},60] (* Harvey P. Dale, Jul 18 2021 *)
  • PARI
    concat(0, vector(40, n, k=0; forpart(p=3*n, k++, , [4,4]); k))
    
  • PARI
    concat([0,0], Vec(x^2*(x^2+2)*(x^2+x+1)/((x-1)^4*(x+1)^2*(x^2+1)) + O(x^100)))

Formula

G.f.: x^2*(x^2+2)*(x^2+x+1) / ((x-1)^4*(x+1)^2*(x^2+1)).
a(n) = (6*n^3+6*n^2-3*n-5+(3*n+1)*(-1)^n+2*((-1)^((2*n-1+(-1)^n)/4)+(-1)^((2*n+1-(-1)^n)/4)))/32. - Luce ETIENNE, Feb 17 2017

A256314 Number of partitions of 3n into exactly 5 parts.

Original entry on oeis.org

0, 0, 1, 5, 13, 30, 57, 101, 164, 255, 377, 540, 748, 1014, 1342, 1747, 2233, 2818, 3507, 4319, 5260, 6351, 7599, 9027, 10642, 12470, 14518, 16814, 19366, 22204, 25337, 28796, 32591, 36756, 41301, 46262, 51649, 57501, 63829, 70673, 78045, 85987, 94512
Offset: 0

Views

Author

Colin Barker, Mar 23 2015

Keywords

Examples

			For n=3 the 5 partitions of 3*3 = 9 are [1,1,1,1,5], [1,1,1,2,4], [1,1,1,3,3], [1,1,2,2,3] and [1,2,2,2,2].
		

Crossrefs

Programs

  • Mathematica
    Table[Length[IntegerPartitions[3n,{5}]],{n,0,50}] (* Harvey P. Dale, Jul 21 2019 *)
  • PARI
    concat(0, vector(40, n, k=0; forpart(p=3*n, k++, , [5,5]); k))
    
  • PARI
    concat([0,0], Vec(-x^2*(2*x^7+3*x^6+4*x^5+5*x^4+6*x^3+3*x^2+3*x+1) / ((x-1)^5*(x+1)^2*(x^2+1)*(x^4+x^3+x^2+x+1)) + O(x^100)))

Formula

G.f.: -x^2*(2*x^7+3*x^6+4*x^5+5*x^4+6*x^3+3*x^2+3*x+1) / ((x-1)^5*(x+1)^2*(x^2+1)*(x^4+x^3+x^2+x+1)).

A331952 a(n) = (-7 + (-1)^(1+n) + 6*n^2) / 8.

Original entry on oeis.org

-1, 0, 2, 6, 11, 18, 26, 36, 47, 60, 74, 90, 107, 126, 146, 168, 191, 216, 242, 270, 299, 330, 362, 396, 431, 468, 506, 546, 587, 630, 674, 720, 767, 816, 866, 918, 971, 1026, 1082, 1140, 1199, 1260, 1322, 1386, 1451, 1518, 1586, 1656, 1727, 1800, 1874, 1950, 2027
Offset: 0

Views

Author

Paul Curtz, Feb 02 2020

Keywords

Comments

a(n+1) is once in the hexagonal spiral in A330707. a(n+2) is twice in the same spiral.
a(n) has one odd followed by three evens.
Difference table:
-1, 0, 2, 6, 11, 18, 26, 36, ... = a(n)
1, 2, 4, 5, 7, 8, 10, 11, ... = A001651(n+1)
1, 2, 1, 2, 1, 2, 1, 2, ... = A000034.

Examples

			G.f. = -1 + 2*x^2 + 6*x^3 + 11*x^4 + 18*x^5 + 26*x^6 + 36*x^7 + 47*x^8 + ... - _Michael Somos_, Sep 08 2023
		

Crossrefs

Equals 2 less than A084684, 1 less than A077043, and 1 more than A276382(n-1). - Greg Dresden, Feb 22 2020

Programs

  • Magma
    a:=[-1,0,2,6]; [n le 4 select a[n] else 2*Self(n-1)-2*Self(n-3)+Self(n-4): n in [1..45]]; // Marius A. Burtea, Feb 02 2020
    
  • Mathematica
    LinearRecurrence[{2, 0, -2, 1}, {-1, 0, 2, 6}, 100] (* Amiram Eldar, Feb 02 2020 *)
    a[n_] := Floor[(n^2 - 1)*3/4]; (* Michael Somos, Sep 08 2023 *)
  • PARI
    Vec(-(1 - 2*x - 2*x^2) / ((1 - x)^3*(1 + x)) + O(x^40)) \\ Colin Barker, Feb 03 2020
    
  • PARI
    {a(n) = (n^2 - 1)*3\4}; /* Michael Somos, Sep 08 2023 */

Formula

a(-n) = a(n).
a(20+n) - a(n) = 30*(10+n).
a(2+n) = a(n) + 3*(1+n), a(0)=-1 and a(1)=0.
a(4*n) = 12*n^2 - 1, a(1+4*n) = 6*n*(1+2*n), a(2+4*n) = 2 + 12*n*(1+n), a(3+4*n) = 6*(1+n)*(1+2*n) for n>= 0.
From Colin Barker, Feb 02 2020: (Start)
G.f.: -(1 - 2*x - 2*x^2) / ((1 - x)^3*(1 + x)).
a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4) for n>3.
a(n) = (-7 + (-1)^(1+n) + 6*n^2) / 8.
(End)
E.g.f.: (1/8)*(exp(x)*(6*x^2 + 6*x - 7) - exp(-x)). - Stefano Spezia, Feb 02 2020 after Colin Barker
a(n) = floor((n^2 - 1)*3/4). - Michael Somos, Sep 09 2023

Extensions

a(42)-a(52) from Stefano Spezia, Feb 02 2020

A133458 The size of the largest antichain in the 7-dimensional hypercubic lattice of size n; also the coefficient of x^floor(7*(n-1)/2) in (1 + x + ... + x^(n-1))^7.

Original entry on oeis.org

1, 35, 393, 2128, 8135, 24017, 60691, 134512, 273127, 512365, 908755, 1528688, 2473325, 3852919, 5832765, 8582336, 12354469, 17395119, 24072133, 32726960, 43874139, 57971221, 75715487, 97702640, 124853275, 157924585, 198105727
Offset: 1

Views

Author

Leonid Chindelevitch (leonidus(AT)mit.edu), Dec 22 2007

Keywords

Comments

The middle coefficients for dimension d>=1 are in A000012, A000027, A077043, A005900, A077044, A071816, here, the d-th row in A077042.
For d=8 the sequence starts 1, 70, 1107, 8092, 38165, 135954, 398567, 1012664, 2306025, ... and for d=9 it starts 1, 126, 3139, 30276, 180325, 767394, 2636263, 7635987, 19610233, ... - R. J. Mathar, Sep 04 2011

Crossrefs

Programs

  • Magma
    [-25*(-1)^n/512 +2261*n^2/23040 +25/512 +5887*n^6/11520 -77*(-1)^n*n^4/1536 +847*n^4/4608 -91*(-1)^n*n^2/1536 : n in [1..40]]; // Vincenzo Librandi, Sep 07 2011
  • Maple
    f:=(L,d)->(sum(x^k,k=0..L-1))^d; A:=[seq(coeff(f(j,7),x,floor(7*(j-1)/2)),j=1..25)];
    A133458 := proc(n) -25/512*(-1)^n +2261/23040*n^2 -91/1536*(-1)^n*n^2 -77/1536*(-1)^n*n^4 +847/4608*n^4 +5887/11520*n^6 +25/512 ; end proc: # R. J. Mathar, Sep 05 2011

Formula

From R. J. Mathar, Feb 19 2010: (Start)
a(n)= 2*a(n-1) +4*a(n-2) -10*a(n-3) -5*a(n-4) +20*a(n-5) -20*a(n-7) +5*a(n-8) +10*a(n-9) -4*a(n-10) -2*a(n-11) +a(n-12).
G.f.: x*(1+33*x +319*x^2 +1212*x^3 +2662*x^4 +3320*x^5 +2662*x^6 +1212*x^7 +319*x^8 +33*x^9 +x^10)/ ((1+x)^5 * (1-x)^7).
a(n) = -25*(-1)^n/512 +2261*n^2/23040 +25/512 +5887*n^6/11520 -77*(-1)^n*n^4/1536 +847*n^4/4608 -91*(-1)^n*n^2/1536. (End)

Extensions

More terms from R. J. Mathar, Feb 19 2010

A212503 Number of (w,x,y,z) with all terms in {1,...,n} and w<2x and y<2z.

Original entry on oeis.org

0, 1, 9, 49, 144, 361, 729, 1369, 2304, 3721, 5625, 8281, 11664, 16129, 21609, 28561, 36864, 47089, 59049, 73441, 90000, 109561, 131769, 157609, 186624, 219961, 257049, 299209, 345744, 398161, 455625, 519841, 589824, 667489, 751689
Offset: 0

Views

Author

Clark Kimberling, May 19 2012

Keywords

Comments

For a guide to related sequences, see A211795.

Crossrefs

Cf. A211795.

Programs

  • Mathematica
    t = Compile[{{n, _Integer}}, Module[{s = 0},
    (Do[If[w < 2 x && y < 2 z, s = s + 1],
    {w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
    Map[t[#] &, Range[0, 40]]   (* A212503 *)
    LinearRecurrence[{2,2,-6,0,6,-2,-2,1},{0,1,9,49,144,361,729,1369},40] (* Harvey P. Dale, Jun 14 2017 *)

Formula

a(n) = (A077043(n))^2.
a(n) = 2*a(n-1)+2*a(n-2)-6*a(n-3)+6*a(n-5)-2*a(n-6)-2*a(n-7)+a(n-8).
G.f.: x*(1+x+x^2)*(1+6*x+22*x^2+6*x^3+x^4)/((1+x)^3*(1-x)^5). [Bruno Berselli, May 31 2012]
Previous Showing 21-30 of 40 results. Next