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 1-10 of 14 results. Next

A003763 Number of (undirected) Hamiltonian cycles on a 2n X 2n square grid of points.

Original entry on oeis.org

1, 6, 1072, 4638576, 467260456608, 1076226888605605706, 56126499620491437281263608, 65882516522625836326159786165530572, 1733926377888966183927790794055670829347983946, 1020460427390768793543026965678152831571073052662428097106
Offset: 1

Views

Author

Jeffrey Shallit, Feb 14 2002

Keywords

Comments

Orientation of the path is not important; you can start going either clockwise or counterclockwise.
The number is zero for a 2n+1 X 2n+1 grid (but see A222200).
These are also called "closed rook tours".

Examples

			a(1) = 1 because there is only one such path visiting all nodes of a square.
		

References

  • F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.

Crossrefs

Other enumerations of Hamiltonian cycles on a square grid: A120443, A140519, A140521, A222200, A222201.

Formula

a(n) = A321172(2n,2n). - Robert FERREOL, Apr 01 2019

Extensions

Two more terms from Andre Poenitz [André Pönitz] and Peter Tittmann (poenitz(AT)htwm.de), Mar 03 2003
a(8) from Herman Jamke (hermanjamke(AT)fastmail.fm), Nov 21 2006
a(9) and a(10) from Jesper L. Jacobsen (jesper.jacobsen(AT)u-psud.fr), Dec 12 2007

A332307 Array read by antidiagonals: T(m,n) is the number of (undirected) Hamiltonian paths in the m X n grid graph.

Original entry on oeis.org

1, 1, 1, 1, 4, 1, 1, 8, 8, 1, 1, 14, 20, 14, 1, 1, 22, 62, 62, 22, 1, 1, 32, 132, 276, 132, 32, 1, 1, 44, 336, 1006, 1006, 336, 44, 1, 1, 58, 688, 3610, 4324, 3610, 688, 58, 1, 1, 74, 1578, 12010, 26996, 26996, 12010, 1578, 74, 1, 1, 92, 3190, 38984, 109722, 229348, 109722, 38984, 3190, 92, 1
Offset: 1

Views

Author

Andrew Howroyd, Feb 09 2020

Keywords

Examples

			Array begins:
================================================
m\n | 1  2   3     4      5       6        7
----+-------------------------------------------
  1 | 1  1   1     1      1       1        1 ...
  2 | 1  4   8    14     22      32       44 ...
  3 | 1  8  20    62    132     336      688 ...
  4 | 1 14  62   276   1006    3610    12010 ...
  5 | 1 22 132  1006   4324   26996   109722 ...
  6 | 1 32 336  3610  26996  229348  1620034 ...
  7 | 1 44 688 12010 109722 1620034 13535280 ...
  ...
		

Crossrefs

Formula

T(n,m) = T(m,n).

A339190 Square array T(n,k), n >= 2, k >= 2, read by antidiagonals, where T(n,k) is the number of (undirected) Hamiltonian cycles on the n X k king graph.

Original entry on oeis.org

3, 4, 4, 8, 16, 8, 16, 120, 120, 16, 32, 744, 2830, 744, 32, 64, 4922, 50354, 50354, 4922, 64, 128, 31904, 1003218, 2462064, 1003218, 31904, 128, 256, 208118, 19380610, 139472532, 139472532, 19380610, 208118, 256, 512, 1354872, 378005474, 7621612496, 22853860116, 7621612496, 378005474, 1354872, 512
Offset: 2

Views

Author

Seiichi Manyama, Nov 27 2020

Keywords

Examples

			Square array T(n,k) begins:
   3,     4,        8,         16,            32,               64, ...
   4,    16,      120,        744,          4922,            31904, ...
   8,   120,     2830,      50354,       1003218,         19380610, ...
  16,   744,    50354,    2462064,     139472532,       7621612496, ...
  32,  4922,  1003218,  139472532,   22853860116,    3601249330324, ...
  64, 31904, 19380610, 7621612496, 3601249330324, 1622043117414624, ...
		

Crossrefs

Rows and columns 3..5 give A339200, A339201, A339202.
Main diagonal gives A140519.

Programs

  • Python
    # Using graphillion
    from graphillion import GraphSet
    def make_nXk_king_graph(n, k):
        grids = []
        for i in range(1, k + 1):
            for j in range(1, n):
                grids.append((i + (j - 1) * k, i + j * k))
                if i < k:
                    grids.append((i + (j - 1) * k, i + j * k + 1))
                if i > 1:
                    grids.append((i + (j - 1) * k, i + j * k - 1))
        for i in range(1, k * n, k):
            for j in range(1, k):
                grids.append((i + j - 1, i + j))
        return grids
    def A339190(n, k):
        universe = make_nXk_king_graph(n, k)
        GraphSet.set_universe(universe)
        cycles = GraphSet.cycles(is_hamilton=True)
        return cycles.len()
    print([A339190(j + 2, i - j + 2) for i in range(10 - 1) for j in range(i + 1)])

Formula

T(n,k) = T(k,n).

A359855 Array read by antidiagonals: T(n,k) is the number of Hamiltonian cycles in the stacked prism graph P_n X C_k, n >= 1, k >= 2.

Original entry on oeis.org

1, 1, 4, 1, 3, 4, 1, 6, 6, 4, 1, 5, 22, 12, 4, 1, 8, 30, 82, 24, 4, 1, 7, 86, 160, 306, 48, 4, 1, 10, 126, 776, 850, 1142, 96, 4, 1, 9, 318, 1484, 7010, 4520, 4262, 192, 4, 1, 12, 510, 6114, 18452, 63674, 24040, 15906, 384, 4, 1, 11, 1182, 12348, 126426, 229698, 578090, 127860, 59362, 768, 4
Offset: 1

Views

Author

Andrew Howroyd, Feb 18 2025

Keywords

Comments

The case for P_n X C_2 is determined using a double edge for C_2.

Examples

			Array begins:
=========================================================
n\k | 2   3     4      5       6        7          8 ...
----+---------------------------------------------------
  1 | 1   1     1      1       1        1          1 ...
  2 | 4   3     6      5       8        7         10 ...
  3 | 4   6    22     30      86      126        318 ...
  4 | 4  12    82    160     776     1484       6114 ...
  5 | 4  24   306    850    7010    18452     126426 ...
  6 | 4  48  1142   4520   63674   229698    2588218 ...
  7 | 4  96  4262  24040  578090  2861964   53055038 ...
  8 | 4 192 15906 127860 5247824 35663964 1087362018 ...
   ...
		

Crossrefs

Rows 1..2 are A000012, A103889(n+1).
Cf. A222196 (order of recurrences), A222197 (main diagonal), A270273, A321172.

A006864 Number of Hamiltonian cycles in P_4 X P_n.

Original entry on oeis.org

0, 1, 2, 6, 14, 37, 92, 236, 596, 1517, 3846, 9770, 24794, 62953, 159800, 405688, 1029864, 2614457, 6637066, 16849006, 42773094, 108584525, 275654292, 699780452, 1776473532, 4509783909, 11448608270, 29063617746, 73781357746, 187302518353, 475489124976, 1207084188912
Offset: 1

Views

Author

kwong(AT)cs.fredonia.edu (Harris Kwong), N. J. A. Sloane, Simon Plouffe and Frans J. Faase

Keywords

Comments

Wazir tours on a 4 X n grid. There are two closed loops for a 4x4 board, appearing as an H and a C, for example. - Ed Pegg Jr, Sep 07 2010

References

  • F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.
  • Kwong, Y. H. H.; Enumeration of Hamiltonian cycles in P_4 X P_n and P_5 X P_n. Ars Combin. 33 (1992), 87-96.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Row/column 4 of A321172.

Programs

  • Mathematica
    LinearRecurrence[{2, 2, -2, 1}, {0, 1, 2, 6}, 50] (* Paolo Xausa, Jul 01 2025 *)
  • Maxima
    a(n):=sum ( sum ( binomial(k,j) *sum (binomial(j, i-j)*2^j *binomial(k-j,n-i-3*(k-j))*(-2)^(4*(k-j)-(n-i)), i,j,n-k+j) , j,0,k) , k,1,n ); /* Vladimir Kruchinin, Aug 04 2010 */

Formula

a(n) = 2*a(n-1) + 2*a(n-2) - 2*a(n-3) + a(n-4).
G.f.: x^2/(1-2x-2x^2+2x^3-x^4). - R. J. Mathar, Dec 16 2008
a(n)=sum ( sum ( binomial(k,j) * sum (binomial(j, i-j)*2^j *binomial(k-j,n-i-3*(k-j))*(-2)^(4*(k-j)-(n-i)), i,j,n-k+j) , j,0,k) , k,1,n ), n>0. - Vladimir Kruchinin, Aug 04 2010
a(n) = Sum_{k=1..n-1} A181688(k). - Kevin McShane, Aug 04 2019

A145418 Number of Hamiltonian cycles in P_8 X P_n.

Original entry on oeis.org

0, 1, 8, 236, 1696, 32675, 301384, 4638576, 49483138, 681728204, 7837276902, 102283239429, 1220732524976, 15513067188008, 188620289493918, 2365714170297014, 29030309635705054, 361749878496079778, 4459396682866920534, 55391169255983979555, 684363209103066303906
Offset: 1

Views

Author

N. J. A. Sloane, Feb 03 2009

Keywords

References

  • F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.

Crossrefs

Row/column 8 of A321172.

Formula

Recurrence:
a(1) = 0,
a(2) = 1,
a(3) = 8,
a(4) = 236,
a(5) = 1696,
a(6) = 32675,
a(7) = 301384,
a(8) = 4638576,
a(9) = 49483138,
a(10) = 681728204,
a(11) = 7837276902,
a(12) = 102283239429,
a(13) = 1220732524976,
a(14) = 15513067188008,
a(15) = 188620289493918,
a(16) = 2365714170297014,
a(17) = 29030309635705054,
a(18) = 361749878496079778,
a(19) = 4459396682866920534,
a(20) = 55391169255983979555,
a(21) = 684363209103066303906,
a(22) = 8487168277379774266411,
a(23) = 104976660007043902770814,
a(24) = 1300854247070195164448395,
a(25) = 16098959403506801921858124,
a(26) = 199418506963731877069653608,
a(27) = 2468612432237087475265791106,
a(28) = 30572953033472980838613625389,
a(29) = 378515201134457658578140498814,
a(30) = 4687342384540802154353083423651,
a(31) = 58036542374043013796287237537528,
a(32) = 718661780960820074611282900026324,
a(33) = 8898436384928204979882033571220340,
a(34) = 110186062841343288284017151289070451,
a(35) = 1364340857418682291195543074012508456,
a(36) = 16893937354451697990213722467612836695,
a(37) = 209185026496655279949634983839901418774,
a(38) = 2590216891342324056714821054881440813215,
a(39) = 32072851564440568180804318145788811014976,
a(40) = 397138412927090582354377476417693090903768,
a(41) = 4917498017559613255667946000320694921175130,
a(42) = 60890272030773519479287882832089863209466478,
a(43) = 753964042571110322417001735829736156594209380,
a(44) = 9335854145287983656933756936219959893935498622,
a(45) = 115599774527478742012501648761874199775452411672,
a(46) = 1431397531309770867365502551162804883408923187965,
a(47) = 17724063449625564471462425816551511960390740556400,
a(48) = 219465622040057380709984287099015972930644329156424,
a(49) = 2717500192865830096645192106030659520142409708395450,
a(50) = 33649045694807090450997457881543310615794538874090382,
a(51) = 416654292509213357722564031894407450765035835407734706,
a(52) = 5159160169073567278327353311624938215272772058329334389,
a(53) = 63882533593051394161814876759814129552293422016852019728,
a(54) = 791016010339998093452532578418540484158488096782539430286,
a(55) = 9794638258031421885388598947932945990242328205117007130718,
a(56) = 121280656298395438005330895082043790844069204530565536980402,
a(57) = 1501739723290424387359817153191514221861132297169144591119746,
a(58) = 18595069417782079319375695239542203044044419158097555496277590,
a(59) = 230250687548524273220393339819664989761608497977237213691651494,
a(60) = 2851044985755900792432116853155397844049903269953868448269465911,
a(61) = 35302641500328319561839557836179860373923985349499838565583491438,
a(62) = 437129721450539018107540085474755888131298517879956664876467411931,
a(63) = 5412693919496858591306748921846182243342130551030595689565457284562,
a(64) = 67021879478670244241238920776850020175011969240135534404057401625317,
a(65) = 829888479044613035646707314461069153586129302554576136417149736843676,
a(66) = 10275970973805259625689798376883875013812168498330812425399678612679778, and
a(n) = 16a(n-1) + 59a(n-2) - 1824a(n-3) + 3898a(n-4) + 55218a(n-5)
- 243282a(n-6) - 545916a(n-7) + 4861689a(n-8) - 2576498a(n-9) - 43488068a(n-10)
+ 94333210a(n-11) + 141446298a(n-12) - 752431432a(n-13) + 377840445a(n-14) + 2789611474a(n-15)
- 4656548198a(n-16) - 5258354388a(n-17) + 18170944298a(n-18) + 3512822542a(n-19) - 45026326037a(n-20)
+ 9980240588a(n-21) + 84208620015a(n-22) - 44876200668a(n-23) - 121497215791a(n-24) + 102246696772a(n-25)
+ 117755621290a(n-26) - 145213823124a(n-27) - 60571088405a(n-28) + 136877858022a(n-29) + 3649170978a(n-30)
- 100110796416a(n-31) + 42689760462a(n-32) + 39482359310a(n-33) - 72614614806a(n-34) + 27495494908a(n-35)
+ 40732692257a(n-36) - 38863698070a(n-37) + 9092063794a(n-38) + 5076214026a(n-39) - 9600155591a(n-40)
+ 4294619636a(n-41) - 1463899423a(n-42) + 4331661320a(n-43) - 2669382577a(n-44) - 998576578a(n-45)
+ 1722204514a(n-46) - 1646502104a(n-47) + 1188567443a(n-48) - 143652474a(n-49) - 380794039a(n-50)
- 27735814a(n-51) + 132682964a(n-52) + 79877148a(n-53) + 41238077a(n-54) - 16408310a(n-55)
- 42867025a(n-56) - 18129698a(n-57) + 4261277a(n-58) + 4951334a(n-59) + 985598a(n-60)
- 103168a(n-61) - 13629a(n-62) + 34282a(n-63) + 6952a(n-64) - 532a(n-65)
+ 36a(n-66).

A145401 Number of Hamiltonian cycles in P_6 X P_n.

Original entry on oeis.org

0, 1, 4, 37, 154, 1072, 5320, 32675, 175294, 1024028, 5668692, 32463802, 181971848, 1033917350, 5824476298, 32989068162, 186210666468, 1053349394128, 5950467515104, 33643541208290, 190115484271760, 1074685815276400, 6073680777522430, 34330607094625734
Offset: 1

Views

Author

N. J. A. Sloane, Feb 03 2009

Keywords

References

  • F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.

Crossrefs

Row/column 6 of A321172.

Programs

  • Maple
    a:= n-> (Matrix([32675, 5320, 1072, 154, 37, 4, 1, 0, 1/2, 0, -5, -16, 51, 869/2]). Matrix(14, (i, j)-> if i=j-1 then 1 elif j=1 then [5, 14, -63, 12, 90, -35, -66, 118, -8, -82, 42, 28, -4, 2][i] else 0 fi)^n)[1,9]: seq(a(n), n=1..30);  # Alois P. Heinz, Oct 24 2009
  • Mathematica
    a[n_] := ({32675, 5320, 1072, 154, 37, 4, 1, 0, 1/2, 0, -5, -16, 51, 869/2 }.MatrixPower[Table[If[i == j-1, 1, If[j == 1, {5, 14, -63, 12, 90, -35, -66, 118, -8, -82, 42, 28, -4, 2}[[i]], 0]], {i, 1, 14}, {j, 1, 14}], n] )[[9]]; Table[a[n], {n, 1, 30}] (* Jean-François Alcover, Feb 14 2016, after Alois P. Heinz *)

Formula

Recurrence: a(1) = 0,
a(2) = 1,
a(3) = 4,
a(4) = 37,
a(5) = 154,
a(6) = 1072,
a(7) = 5320,
a(8) = 32675,
a(9) = 175294,
a(10) = 1024028,
a(11) = 5668692,
a(12) = 32463802,
a(13) = 181971848,
a(14) = 1033917350, and
a(n) = 5a(n-1) +14a(n-2) -63a(n-3) +12a(n-4) +90a(n-5) -35a(n-6) -66a(n-7) +118a(n-8) -8a(n-9) -82a(n-10) +42a(n-11) +28a(n-12) -4a(n-13) +2a(n-14).
G.f.: -x^2*(x -1)*(x^11 -x^10 +3*x^9 +12*x^8 -3*x^7 -3*x^4 +21*x^3 -3*x^2 -1)/(2*x^14 -4*x^13 +28*x^12 +42*x^11 -82*x^10 -8*x^9 +118*x^8 -66*x^7- 35*x^6 +90*x^5 +12*x^4 -63*x^3 +14*x^2 +5*x -1). [Colin Barker, Aug 31 2012]

Extensions

More terms from Alois P. Heinz, Oct 24 2009

A145416 Number of Hamiltonian cycles in P_7 X P_2n.

Original entry on oeis.org

1, 92, 5320, 301384, 17066492, 966656134, 54756073582, 3101696069920, 175698206778318, 9952578156814524, 563772503196695338, 31935387285412942410, 1809007988782552388490, 102472842263117124008066, 5804663918990466729365476, 328810272735298761062754308
Offset: 1

Views

Author

N. J. A. Sloane, Feb 03 2009

Keywords

References

  • F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.

Crossrefs

Cf. A321172.

Formula

Recurrence:
a(1) = 1,
a(2) = 92,
a(3) = 5320,
a(4) = 301384,
a(5) = 17066492,
a(6) = 966656134,
a(7) = 54756073582,
a(8) = 3101696069920,
a(9) = 175698206778318,
a(10) = 9952578156814524,
a(11) = 563772503196695338,
a(12) = 31935387285412942410,
a(13) = 1809007988782552388490,
a(14) = 102472842263117124008066,
a(15) = 5804663918990466729365476,
a(16) = 328810272735298761062754308,
a(17) = 18625745945872429428768223714,
a(18) = 1055071695766249759732087999456, and
a(n) = 85a(n-1) - 1932a(n-2) + 20403a(n-3) - 116734a(n-4) + 386724a(n-5)
- 815141a(n-6) + 1251439a(n-7) - 1690670a(n-8) + 2681994a(n-9)
- 4008954a(n-10) + 3390877a(n-11) - 1036420a(n-12) - 178842a(n-13)
+ 92790a(n-14) + 17732a(n-15) - 5972a(n-16) + 1728a(n-17) + 144a(n-18).

Extensions

Recurrence corrected by Frans J. Faase, Feb 04 2009

A180504 Number of Hamiltonian cycles in P_10 X P_n.

Original entry on oeis.org

0, 1, 16, 1517, 18684, 1024028, 17066492, 681728204, 13916993782, 467260456608, 10754797724124, 328076475659033, 8091313110371792, 233977398720987284, 6002042996016384360, 168435972906750526954, 4418118886987754341770, 121913396076344218930045
Offset: 1

Views

Author

Artem M. Karavaev, Sep 09 2010

Keywords

Comments

The linear recurrence for this sequence has order 346. It is too large to be posted here.

Crossrefs

Row/column 10 of A321172.
Cf. A160149.

Extensions

a(16) onwards from Andrew Howroyd, Dec 13 2024

A180505 Number of Hamiltonian cycles in P_11 X P_2n.

Original entry on oeis.org

1, 3846, 5668692, 7837276902, 10754797724124, 14746957510647992, 20223692320200140940, 27738606105535271640888, 38049128385426605236700966, 52194036750499722755908743018, 71598455565101470929617326988084, 98217523834843365306426848969040826, 134733398926676359394934062807293332148
Offset: 1

Views

Author

Artem M. Karavaev, Sep 09 2010

Keywords

Comments

The linear recurrence for this sequence has order 671. It is too large to be posted here.

Crossrefs

Extensions

a(11)-a(13) from Seiichi Manyama, Mar 29 2020
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