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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A264071 T(n,k) = number of (n+1) X (k+1) arrays of permutations of 0..(n+1)*(k+1)-1 with each element having index change +-(.,.) 0,0 1,1 or 1,2.

Original entry on oeis.org

2, 5, 4, 13, 21, 8, 34, 121, 89, 16, 89, 605, 1210, 377, 32, 233, 3025, 12100, 12100, 1597, 64, 610, 15125, 131890, 239580, 121000, 6765, 128, 1597, 75625, 1445345, 5645376, 4745620, 1210000, 28657, 256, 4181, 378125, 15892745, 130697424, 242621698, 94000060, 12100000, 121393, 512
Offset: 1

Views

Author

R. H. Hardin, Nov 02 2015

Keywords

Examples

			Table starts:
     2       5          13             34                89                  233
     4      21         121            605              3025                15125
     8      89        1210          12100            131890              1445345
    16     377       12100         239580           5645376            130697424
    32    1597      121000        4745620         242621698          11909009849
    64    6765     1210000       94000060       10427064769        1084282319384
   128   28657    12100000     1861931060      448121165789       98725402363225
   256  121393   121000000    36880691100    19258783041289     8989061417123964
   512  514229  1210000000   730524027860   827679549612058   818464496640651553
  1024 2178309 12100000000 14470047586940 35570961850254336 74522143720797473932
  ...
Some solutions for n=3 k=4:
..0..8..9..3..4....6..1..2..3..4....7..8..2..3..4....0..8..2..3..4
..5.13..7..1..2...11.13..0..8..9...12..6..0..1..9....5..6..7..1..9
.16.11.18..6.14...10..5.19..7.14...17..5.18.13.14...17.18.12.13.14
.15.10.17.12.19...15.16.17.18.12...15.16.10.11.19...15.16.10.11.19
		

Crossrefs

Main diagonal is A264066.
Columns 1,2 and 4..7 are A000079, A015448(n+1), A264067, A264068, A264069, A264070.
Rows 1 and 3..7 are A001519(n+1), A264072, A264073, A264074, A264075, A264076.

Formula

Empirical for column k:
k=1: a(n) = 2*a(n-1)
k=2: a(n) = 4*a(n-1) +a(n-2)
k=3: a(n) = 10*a(n-1) for n>2
k=4: a(n) = 19*a(n-1) +16*a(n-2) for n>3
k=5: a(n) = 43*a(n-1) -43*a(n-3) +a(n-4) for n>5
k=6: a(n) = 87*a(n-1) +374*a(n-2) -470*a(n-3) +207*a(n-4) +3*a(n-5) for n>7
k=7: a(n) = 191*a(n-1) +1102*a(n-2) -7594*a(n-3) -38349*a(n-4) +38507*a(n-5) for n>8
Empirical for row n:
n=1: a(n) = 3*a(n-1) -a(n-2)
n=2: a(n) = 5*a(n-1) for n>3
n=3: a(n) = 12*a(n-1) -12*a(n-2) +12*a(n-3) -12*a(n-4) +a(n-5) for n>7
n=4: a(n) = 24*a(n-1) -19*a(n-2) -11*a(n-3) +36*a(n-4) +3*a(n-5) for n>9
n=5: [order 14] for n>19
n=6: [order 10] for n>19

Extensions

Name corrected by Andrew Howroyd, Mar 25 2025

A134504 a(n) = Fibonacci(7n + 6).

Original entry on oeis.org

8, 233, 6765, 196418, 5702887, 165580141, 4807526976, 139583862445, 4052739537881, 117669030460994, 3416454622906707, 99194853094755497, 2880067194370816120, 83621143489848422977, 2427893228399975082453
Offset: 0

Views

Author

Artur Jasinski, Oct 28 2007

Keywords

Crossrefs

Programs

Formula

G.f.: (-8-x) / (-1 + 29*x + x^2). - R. J. Mathar, Jul 04 2011
a(n) = A000045(A017053(n)). - Michel Marcus, Nov 08 2013
a(n) = 29*a(n-1) + a(n-2). - Wesley Ivan Hurt, Mar 15 2023

Extensions

Offset changed from 1 to 0 by Vincenzo Librandi, Apr 17 2011

A154626 a(n) = 2^n*A001519(n).

Original entry on oeis.org

1, 2, 8, 40, 208, 1088, 5696, 29824, 156160, 817664, 4281344, 22417408, 117379072, 614604800, 3218112512, 16850255872, 88229085184, 461973487616, 2418924584960, 12665653559296, 66318223015936, 347246723858432, 1818207451086848, 9520257811087360
Offset: 0

Views

Author

Paul Barry, Jan 13 2009

Keywords

Comments

Hankel transform of 1,1,3,11,45,... (see A026375). Binomial transform of A015448.
From Gary W. Adamson, Jul 22 2016: (Start)
A production matrix for the sequence is M =
1, 1, 0, 0, 0, ...
1, 0, 5, 0, 0, ...
1, 0, 0, 5, 0, ...
1, 0, 0, 0, 5, ...
...
Take powers of M, extracting the upper left terms; getting
the sequence starting (1, 1, 2, 8, 40, 208, ...). (End)
The sequence is N=5 in an infinite set of INVERT transforms of powers of N prefaced with a "1". (1, 2, 8, 40, ...) is the INVERT transform of (1, 1, 5, 25, 125, ...). The first six of such sequences are shown in A006012 (N=3). - Gary W. Adamson, Jul 24 2016
From Gary W. Adamson, Jul 27 2016: (Start)
The sequence is the first in an infinite set in which we perform the operation for matrix M (Cf. Jul 22 2016), but change the left border successively from (1, 1, 1, 1, ...) then to (1, 2, 2, 2, ...), then (1, 3, 3, 3, ...) ...; generally (1, N, N, N, ...). Extracting the upper left terms of each matrix operation, we obtain the infinite set beginning:
N=1 (A154626): 1, 2, 8, 40, 208, 1088, ...
N=2 (A084120): 1, 3, 15, 81, 441, 1403, ...
N=3 (A180034): 1, 4, 22, 124, 700, 3952, ...
N=4 (A001653): 1, 5, 29, 169, 985, 5741, ...
N=5 (A000400): 1, 6, 36, 216, 1296, 7776, ...
N=6 (A015451): 1, 7, 43, 265, 1633, 10063, ...
N=7 (A180029): 1, 8, 50, 316, 1996, 12608, ...
N=8 (A180028): 1, 9, 57, 369, 1285, 15417, ...
N=9 (.......): 1, 10, 64, 424, 2800, 18496, ...
N=10 (A123361): 1, 11, 71, 481, 3241, 21851, ...
N=11 (.......): 1, 12, 78, 540, 3708, 25488, ...
... Each of the sequences begins (1, (N+1), (7*N + 1),
(40*N + (N-1)^2), ... (End)
The set of infinite sequences shown (Cf. comment of Jul 27 2016), can be generated from the matrices P = [(1,N; 1,5]^n, (N=1,2,3,...) by extracting the upper left terms. Example: N=6 sequence (A015451): (1, 7, 43, 265, ...) can be generated from the matrix P = [(1,6); (1,5)]^n. - Gary W. Adamson, Jul 28 2016

Crossrefs

Programs

  • Magma
    [n le 2 select (n) else 6*Self(n-1)-4*Self(n-2): n in [1..25]]; // Vincenzo Librandi, May 15 2015
    
  • Mathematica
    LinearRecurrence[{6, -4}, {1, 2}, 30] (* Vincenzo Librandi, May 15 2015 *)
  • PARI
    Vec((1-4*x) / (1-6*x+4*x^2) + O(x^30)) \\ Colin Barker, Sep 22 2017

Formula

G.f.: (1 - 4*x) / (1 - 6*x + 4*x^2).
a(n) = A084326(n+1) - 4*A084326(n). - R. J. Mathar, Jul 19 2012
From Colin Barker, Sep 22 2017: (Start)
a(n) = (((3-sqrt(5))^n*(1+sqrt(5)) + (-1+sqrt(5))*(3+sqrt(5))^n)) / (2*sqrt(5)).
a(n) = 6*a(n-1) - 4*a(n-2) for n>1. (End)
E.g.f.: exp(3*x)*(5*cosh(sqrt(5)*x) - sqrt(5)*sinh(sqrt(5)*x))/5. - Stefano Spezia, Aug 26 2025

A287839 Number of words of length n over the alphabet {0,1,...,10} such that no two consecutive terms have distance 9.

Original entry on oeis.org

1, 11, 117, 1247, 13289, 141619, 1509213, 16083463, 171399121, 1826575451, 19465548357, 207441511727, 2210673955769, 23558830139779, 251063019088173, 2675542001860183, 28512861152219041, 303857405535211691, 3238164083417650197, 34508642672922983807
Offset: 0

Views

Author

David Nacin, Jun 07 2017

Keywords

Comments

In general, the number of sequences on {0,1,...,10} such that no two consecutive terms have distance 6+k for k in {0,1,2,3,4} has generating function (-1 - x)/(-1 + 10*x + (2*k+1)*x^2).

Crossrefs

Programs

  • Maple
    a:=proc(n) option remember; if n=0 then 1 elif n=1 then 11 elif n=2 then 117 else 10*a(n-1)+7*a(n-2); fi; end: seq(a(n), n=0..30); # Wesley Ivan Hurt, Nov 25 2017
  • Mathematica
    LinearRecurrence[{10, 7}, {1, 11, 117}, 20]
  • PARI
    Vec((1 + x) / (1 - 10*x - 7*x^2) + O(x^30)) \\ Colin Barker, Nov 25 2017
  • Python
    def a(n):
     if n in [0,1,2]:
      return [1, 11, 117][n]
     return 10*a(n-1) + 7*a(n-2)
    

Formula

For n>2, a(n) = 10*a(n-1) + 7*a(n-2), a(0)=1, a(1)=11, a(2)=117.
G.f.: (-1 - x)/(-1 + 10 x + 7 x^2).
a(n) = (((5-4*sqrt(2))^n*(-3+2*sqrt(2)) + (3+2*sqrt(2))*(5+4*sqrt(2))^n)) / (4*sqrt(2)). - Colin Barker, Nov 25 2017

A097924 a(n) = 4*a(n-1) + a(n-2), n>=2, a(0) = 2, a(1) = 7.

Original entry on oeis.org

2, 7, 30, 127, 538, 2279, 9654, 40895, 173234, 733831, 3108558, 13168063, 55780810, 236291303, 1000946022, 4240075391, 17961247586, 76085065735, 322301510526, 1365291107839, 5783465941882, 24499154875367, 103780085443350, 439619496648767, 1862258072038418
Offset: 0

Views

Author

Creighton Dement, Sep 04 2004; corrected Sep 16 2004

Keywords

Comments

Previous name was: Sequence relates numerators and denominators in the continued fraction convergents to sqrt(5).
Floretion Algebra Multiplication Program, FAMP Code: 2lesforcycseq[ ( - 'i + 'j - i' + j' - 'kk' - 'ik' - 'jk' - 'ki' - 'kj' )*( .5'i + .5i' ) ], 2vesforcycseq = A000004.

Examples

			G.f. = 2 + 7*x + 30*x^2 + 127*x^3 + 538*x^4 + 2279*x^5 + 9654*x^6 + 40895*x^7 + ...
		

Crossrefs

Programs

  • Magma
    I:=[2,7]; [n le 2 select I[n] else 4*Self(n-1) + Self(n-2): n in [1..30]]; // G. C. Greubel, Dec 20 2017
  • Mathematica
    a[n_] := Expand[((2Sqrt[5] + 3)*(2 + Sqrt[5])^n + (2Sqrt[5] - 3)*(2 - Sqrt[5])^n)/(2Sqrt[5])]; Table[ a[n], {n, 0, 20}] (* Robert G. Wilson v, Sep 17 2004 *)
    a[ n_] := (3 I ChebyshevT[ n + 1, -2 I] + 4 ChebyshevT[ n, -2 I]) I^n / 5; (* Michael Somos, Feb 23 2014 *)
    a[ n_] := If[ n < 0, SeriesCoefficient[ (2 + 7 x) / (1 + 4 x - x^2), {x, 0, -n}], SeriesCoefficient[ (2 - x) / (1 - 4 x - x^2), {x, 0, n}]]; (* Michael Somos, Feb 23 2014 *)
    LinearRecurrence[{4,1}, {2,7}, 50] (* G. C. Greubel, Dec 20 2017 *)
  • PARI
    {a(n) = ( 3*I*polchebyshev( n+1, 1, -2*I) + 4*polchebyshev( n, 1, -2*I)) * I^n / 5}; \\ Michael Somos, Feb 23 2014
    
  • PARI
    {a(n) = if( n<0, polcoeff( (2 + 7*x) / (1 + 4*x - x^2) + x * O(x^-n), -n), polcoeff( (2 - x) / (1 - 4*x - x^2) + x * O(x^n), n))}; \\ Michael Somos, Feb 23 2014
    

Formula

a(n) = A001077(n+1) - 2*A001076(n).
A048875(n) + A001077(n+1)/2 = a(n)/2 + A048876(n).
a(n) = ((2*sqrt(5)+3)*(2+sqrt(5))^n + (2*sqrt(5)-3)*(2-sqrt(5))^n)/(2*sqrt(5)).
a(n+1) = A001077(n+1) + A015448(n+2) - Creighton Dement, Mar 08 2005
From Philippe Deléham, Nov 20 2008: (Start)
a(n) = 4*a(n-1) + a(n-2) for n>=2, a(0)=2, a(1)=7.
G.f.: (2-x)/(1-4*x-x^2). (End)
G.f.: G(0)*(2-x)/2, where G(k) = 1 + 1/(1 - x*(8*k + 4 +x)/(x*(8*k + 8 +x) + 1/G(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Feb 15 2014
a(-1 - n) = -(-1)^n * A048875(n). - Michael Somos, Feb 23 2014
E.g.f.: exp(2*x)*(10*cosh(sqrt(5)*x) + 3*sqrt(5)*sinh(sqrt(5)*x))/5. - Stefano Spezia, Aug 21 2025

Extensions

Edited, corrected and extended by Robert G. Wilson v, Sep 17 2004
Better name (using formula from Philippe Deléham) from Joerg Arndt, Feb 16 2014

A134494 a(n) = Fibonacci(6n+2).

Original entry on oeis.org

1, 21, 377, 6765, 121393, 2178309, 39088169, 701408733, 12586269025, 225851433717, 4052739537881, 72723460248141, 1304969544928657, 23416728348467685, 420196140727489673, 7540113804746346429, 135301852344706746049, 2427893228399975082453
Offset: 0

Views

Author

Artur Jasinski, Oct 28 2007

Keywords

Crossrefs

Programs

  • Magma
    [Fibonacci(6*n +2): n in [0..100]]; // Vincenzo Librandi, Apr 17 2011
    
  • Maple
    seq( combinat[fibonacci](6*n+2),n=0..10) ; # R. J. Mathar, Apr 17 2011
  • Mathematica
    Table[Fibonacci[6n+2], {n, 0, 30}]
    Table[ChebyshevU[3*n, 3/2], {n, 0, 20}] (* Vaclav Kotesovec, May 27 2023 *)
  • PARI
    a(n)=fibonacci(6*n+2) \\ Charles R Greathouse IV, Jun 11 2015
    
  • PARI
    Vec((1+3*x)/(1-18*x+x^2) + O(x^100)) \\ Altug Alkan, Jan 24 2016

Formula

From R. J. Mathar, Jul 04 2011: (Start)
G.f.: ( 1+3*x ) / ( 1-18*x+x^2 ).
a(n) = 3*A049660(n)+A049660(n+1). (End)
a(n) = A000045(A016933(n)). - Michel Marcus, Nov 07 2013
a(n) = ((5-3*sqrt(5)+(5+3*sqrt(5))*(9+4*sqrt(5))^(2*n)))/(10*(9+4*sqrt(5))^n). - Colin Barker, Jan 24 2016
a(n) = S(3*n, 3) = S(n,18) + 3*S(n-1,18), with the Chebyshev S polynomials (A049310), S(-1, x) = 0, and S(n, 18) = A049660(n+1). - Wolfdieter Lang, May 08 2023

Extensions

Index in definition corrected by T. D. Noe, Joerg Arndt, Apr 17 2011

A287831 Number of sequences over the alphabet {0,1,...,9} such that no two consecutive terms have distance 8.

Original entry on oeis.org

1, 10, 96, 924, 8892, 85572, 823500, 7924932, 76265388, 733938084, 7063035084, 67970944260, 654116708844, 6294876045156, 60578584659468, 582976518206148, 5610260171812140, 53990200655546148, 519573366930788172, 5000101506310370436, 48118353758378062956
Offset: 0

Views

Author

David Nacin, Jun 02 2017

Keywords

Comments

In general, the number of sequences over the alphabet {0,1,...,9} such that no two consecutive terms have distance 5+k for k in {0,1,2,3,4} is given by a(n) = 9*a(n-1) + 2*k*a(n-2), a(0)=1, a(1)=10.

Crossrefs

Programs

  • Mathematica
    LinearRecurrence[{9, 6}, {1, 10}, 30]
  • Python
    def a(n):
     if n in [0, 1]:
      return [1, 10][n]
     return 9*a(n-1)+6*a(n-2)

Formula

a(n) = 9*a(n-1) + 6*a(n-2), a(0)=1, a(1)=10.
G.f.: (-1 - x)/(-1 + 9*x + 6*x^2).
a(n) = ((1 - 11/sqrt(105))/2)*((9 - sqrt(105))/2)^n + ((1 + 11/sqrt(105))/2)*((9 + sqrt(105))/2)^n.

A013946 Least d for which the number with continued fraction [n,n,n,n...] is in Q(sqrt(d)).

Original entry on oeis.org

5, 2, 13, 5, 29, 10, 53, 17, 85, 26, 5, 37, 173, 2, 229, 65, 293, 82, 365, 101, 445, 122, 533, 145, 629, 170, 733, 197, 5, 226, 965, 257, 1093, 290, 1229, 13, 1373, 362, 61, 401, 1685, 442, 1853, 485, 2029, 530, 2213, 577, 2405, 626, 2605, 677, 2813, 730, 3029, 785, 3253
Offset: 1

Views

Author

Keywords

Comments

Square roots of a(n) are found in the limiting ratios of A000045, A001333, A003688, A015448, A015449, A015451 and so on. I.e., the limiting ratios are the golden ratio, silver mean, bronze ratio and so on. - Mats Granvik, Oct 20 2010

Crossrefs

a(n) = 2 is equivalent to "n is in the sequence A077444", a(n) = 5 is equivalent to "n is in the sequence A002878".

Programs

  • Mathematica
    z = 5000; u = Table[{p, e} = Transpose[FactorInteger[n]];
    Times @@ (p^Mod[e, 2]), {n, z}]; Table[u[[n^2 + 4]], {n, 1, Sqrt[z - 4]}]  (* Clark Kimberling, Jul 20 2015, based on T. D. Noe's program at A007913 *)
  • PARI
    A013946(n)=core(n^2+4)  \\ M. F. Hasler, Dec 08 2010

Formula

a(n) = A007913(n^2+4). - David W. Wilson, Dec 08 2010

Extensions

More terms from David W. Wilson

A134501 a(n) = Fibonacci(7n + 3).

Original entry on oeis.org

2, 55, 1597, 46368, 1346269, 39088169, 1134903170, 32951280099, 956722026041, 27777890035288, 806515533049393, 23416728348467685, 679891637638612258, 19740274219868223167, 573147844013817084101, 16641027750620563662096
Offset: 0

Views

Author

Artur Jasinski, Oct 28 2007

Keywords

Crossrefs

Programs

Formula

From R. J. Mathar, Jul 04 2011: (Start)
G.f.: (-2+3*x) / (-1 + 29*x + x^2).
a(n) = 2*A049667(n+1) - 3*A049667(n). (End)
a(n) = A000045(A017017(n)). - Michel Marcus, Nov 07 2013

Extensions

Offset changed to 0 by Vincenzo Librandi, Apr 16 2011

A134502 a(n) = Fibonacci(7n + 4).

Original entry on oeis.org

3, 89, 2584, 75025, 2178309, 63245986, 1836311903, 53316291173, 1548008755920, 44945570212853, 1304969544928657, 37889062373143906, 1100087778366101931, 31940434634990099905, 927372692193078999176, 26925748508234281076009
Offset: 0

Views

Author

Artur Jasinski, Oct 28 2007

Keywords

Crossrefs

Programs

Formula

From R. J. Mathar, Jul 04 2011: (Start)
G.f.: (-3-2*x) / (-1 + 29*x + x^2).
a(n) = 2*A049667(n) + 3*A049667(n+1). (End)
a(n) = A000045(A017029(n)). - Michel Marcus, Nov 07 2013

Extensions

Offset changed from 1 to 0 by Vincenzo Librandi, Apr 17 2011
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