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 1-9 of 9 results.

A001091 a(n) = 8*a(n-1) - a(n-2); a(0) = 1, a(1) = 4.

Original entry on oeis.org

1, 4, 31, 244, 1921, 15124, 119071, 937444, 7380481, 58106404, 457470751, 3601659604, 28355806081, 223244789044, 1757602506271, 13837575261124, 108942999582721, 857706421400644, 6752708371622431, 53163960551578804
Offset: 0

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Author

Keywords

Comments

a(15+30k)-1 and a(15+30k)+1 are consecutive odd powerful numbers. The first pair is 13837575261124 +- 1. See A076445. - T. D. Noe, May 04 2006
This sequence gives the values of x in solutions of the Diophantine equation x^2 - 15*y^2 = 1. The corresponding y values are in A001090. - Vincenzo Librandi, Nov 12 2010 [edited by Jon E. Schoenfield, May 04 2014]
The square root of 15*(n^2-1) at those numbers = 5 * A136325. - Richard R. Forberg, Nov 22 2013
For the above Diophantine equation x^2-15*y^2=1, x + y = A105426. - Richard R. Forberg, Nov 22 2013
a(n) solves for x in the Diophantine equation floor(3*x^2/5)= y^2. The corresponding y solutions are provided by A136325(n). x + y = A070997(n). - Richard R. Forberg, Nov 22 2013
Except for the first term, values of x (or y) in the solutions to x^2 - 8xy + y^2 + 15 = 0. - Colin Barker, Feb 05 2014

References

  • Bastida, Julio R. Quadratic properties of a linearly recurrent sequence. Proceedings of the Tenth Southeastern Conference on Combinatorics, Graph Theory and Computing (Florida Atlantic Univ., Boca Raton, Fla., 1979), pp. 163--166, Congress. Numer., XXIII-XXIV, Utilitas Math., Winnipeg, Man., 1979. MR0561042 (81e:10009) - From N. J. A. Sloane, May 30 2012
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A001090, A090965, A098269, A322836 (column 4).

Programs

  • GAP
    a:=[1,4];; for n in [3..20] do a[n]:=8*a[n-1]-a[n-2]; od; a; # G. C. Greubel, Aug 26 2019
  • Magma
    R:=PowerSeriesRing(Integers(), 20); Coefficients(R!( (1-4*x)/(1-8*x+x^2) )); // G. C. Greubel, Aug 26 2019
    
  • Mathematica
    LinearRecurrence[{8,-1},{1,4},20] (* Harvey P. Dale, May 01 2014 *)
  • PARI
    a(n)=subst(poltchebi(n),x,4)
    
  • PARI
    a(n)=n=abs(n); polcoeff((1-4*x)/(1-8*x+x^2)+x*O(x^n),n) /* Michael Somos, Jun 07 2005 */
    
  • Sage
    def A001091_list(prec):
        P. = PowerSeriesRing(ZZ, prec)
        return P( (1-4*x)/(1-8*x+x^2) ).list()
    A001091_list(20) # G. C. Greubel, Aug 26 2019
    

Formula

G.f.: A(x) = (1-4*x)/(1-8*x+x^2). - Simon Plouffe in his 1992 dissertation
For all elements x of the sequence, 15*(x^2 -1) is a square. Limit_{n -> infinity} a(n)/a(n-1) = 4 + sqrt(15). - Gregory V. Richardson, Oct 11 2002
a(n) = sqrt(15*((A001090(n))^2)+1).
a(n) = ((4+sqrt(15))^n + (4-sqrt(15))^n)/2.
a(n) = 4*S(n-1, 8) - S(n-2, 8) = (S(n, 8) - S(n-2, 8))/2, n>=1; S(n, x) := U(n, x/2) with Chebyshev's polynomials of the 2nd kind, A049310, with S(-1, x) := 0 and S(-2, x) := -1.
a(n) = T(n, 4) with Chebyshev's polynomials of the first kind; see A053120.
a(n)=a(-n). - Ralf Stephan, Jun 06 2005
a(n)*a(n+3) - a(n+1)*a(n+2) = 120. - Ralf Stephan, Jun 06 2005
From Peter Bala, Feb 19 2022: (Start)
a(n) = Sum_{k = 0..floor(n/2)} 4^(n-2*k)*15^k*binomial(n,2*k).
a(n) = [x^n] (4*x + sqrt(1 + 15*x^2))^n.
The g.f. A(x) satisfies A(2*x) = 1 + x*B'(x)/B(x), where B(x) = 1/sqrt(1 - 16*x + 4*x^2) is the g.f. of A098269.
The Gauss congruences a(n*p^k) == a(n*p^(k-1)) (mod p^k) hold for all primes p >= 3 and positive integers n and k. (End)
From Peter Bala, Aug 17 2022: (Start)
Sum_{n >= 1} 1/(a(n) - (5/2)/a(n)) = 1/3.
Sum_{n >= 1} (-1)^(n+1)/(a(n) + (3/2)/a(n)) = 1/5.
Sum_{n >= 1} 1/(a(n)^2 - 5/2) = 1/3 - 1/sqrt(15). (End)
a(n) = A001090(n+1)-4*A001090(n). - R. J. Mathar, Dec 12 2023

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Aug 25 2000
Chebyshev comments from Wolfdieter Lang, Oct 31 2002

A115066 Chebyshev polynomial of the first kind T(n,x), evaluated at x=n.

Original entry on oeis.org

1, 1, 7, 99, 1921, 47525, 1431431, 50843527, 2081028097, 96450076809, 4993116004999, 285573847759211, 17882714781360001, 1216895030905226413, 89415396036432386311, 7055673735003659189775, 595077930963909484707841, 53421565080956452077519377
Offset: 0

Views

Author

Roger L. Bagula, Mar 01 2006

Keywords

Examples

			a(3) = 99 because T[3, x] = 4x^3 - 3x and T[3, 3] = 4*3^3 - 3*3 = 99.
		

References

  • G. Freud, Orthogonal Polynomials, Pergamon Press, Oxford, 1966, p. 35.
  • M. Rosenblum and J. Rovnyak, Hardy Classes and Operator Theory, Dover, New York, 1985, page 18.
  • G. Szego, Orthogonal polynomials, Amer. Math. Soc., Providence, 1939, p. 29.

Crossrefs

Programs

  • Maple
    with(orthopoly): seq(T(n,n),n=0..17);
  • Mathematica
    Table[ChebyshevT[n, n], {n, 0, 17}] (* Arkadiusz Wesolowski, Nov 17 2012 *)
  • PARI
    A115066(n)=cos(n*acos(n))  \\ M. F. Hasler, Apr 06 2012
    
  • PARI
    a(n) = polchebyshev(n, 1, n); \\ Seiichi Manyama, Dec 28 2018
    
  • PARI
    a(n) = if(n==0, 1, n*sum(k=0, n, (2*n-2)^k*binomial(n+k, 2*k)/(n+k))); \\ Seiichi Manyama, Mar 05 2021

Formula

a(n) = cos(n*arccos(n)).
a(n) ~ 2^(n-1) * n^n. - Vaclav Kotesovec, Jan 19 2019
a(n) = (A323118(n) - A107995(n-2))/2 for n > 1. - Seiichi Manyama, Mar 05 2021
a(n) = n * Sum_{k=0..n} (2*n-2)^k * binomial(n+k,2*k)/(n+k) for n > 0. - Seiichi Manyama, Mar 05 2021
It appears that a(2*n+1) == 0 (mod (2*n+1)^2) and 2*a(4*n+2) == -2 (mod (4*n+2)^4), while for k > 1, 2*a(2^k*(2*n+1)) == 2 (mod (2^k*(2*n+1))^4). - Peter Bala, Feb 01 2022

Extensions

Edited by N. J. A. Sloane, Apr 05 2006

A323182 Square array T(n,k), n >= 0, k >= 0, read by antidiagonals, where T(n,k) is Chebyshev polynomial of the second kind U_{n}(x), evaluated at x=k.

Original entry on oeis.org

1, 1, 0, 1, 2, -1, 1, 4, 3, 0, 1, 6, 15, 4, 1, 1, 8, 35, 56, 5, 0, 1, 10, 63, 204, 209, 6, -1, 1, 12, 99, 496, 1189, 780, 7, 0, 1, 14, 143, 980, 3905, 6930, 2911, 8, 1, 1, 16, 195, 1704, 9701, 30744, 40391, 10864, 9, 0, 1, 18, 255, 2716, 20305, 96030, 242047, 235416, 40545, 10, -1
Offset: 0

Views

Author

Seiichi Manyama, Jan 06 2019

Keywords

Examples

			Square array begins:
   1, 1,    1,     1,      1,      1,       1, ...
   0, 2,    4,     6,      8,     10,      12, ...
  -1, 3,   15,    35,     63,     99,     143, ...
   0, 4,   56,   204,    496,    980,    1704, ...
   1, 5,  209,  1189,   3905,   9701,   20305, ...
   0, 6,  780,  6930,  30744,  96030,  241956, ...
  -1, 7, 2911, 40391, 242047, 950599, 2883167, ...
		

Crossrefs

Mirror of A228161.
Columns 0-19 give A056594, A000027(n+1), A001353(n+1), A001109(n+1), A001090(n+1), A004189(n+1), A004191, A007655(n+2), A077412, A049660(n+1), A075843(n+1), A077421, A077423, A097309, A097311, A097313, A029548, A029547, A144128(n+1), A078987.
Main diagonal gives A323118.
Cf. A179943, A322836 (Chebyshev polynomial of the first kind).

Programs

  • PARI
    T(n,k)  = polchebyshev(n, 2, k);
    matrix(7, 7, n, k, T(n-1,k-1)) \\ Michel Marcus, Jan 07 2019
    
  • PARI
    T(n, k) = sum(j=0, n, (2*k-2)^j*binomial(n+1+j, 2*j+1)); \\ Seiichi Manyama, Mar 03 2021

Formula

T(0,k) = 1, T(1,k) = 2 * k and T(n,k) = 2 * k * T(n-1,k) - T(n-2,k) for n > 1.
T(n, k) = Sum_{j=0..n} (2*k-2)^j * binomial(n+1+j,2*j+1). - Seiichi Manyama, Mar 03 2021

A188644 Array of (k^n + k^(-n))/2 where k = (sqrt(x^2-1) + x)^2 for integers x >= 1.

Original entry on oeis.org

1, 1, 1, 1, 7, 1, 1, 97, 17, 1, 1, 1351, 577, 31, 1, 1, 18817, 19601, 1921, 49, 1, 1, 262087, 665857, 119071, 4801, 71, 1, 1, 3650401, 22619537, 7380481, 470449, 10081, 97, 1, 1, 50843527, 768398401, 457470751, 46099201, 1431431, 18817, 127, 1
Offset: 0

Views

Author

Charles L. Hohn, Apr 06 2011

Keywords

Comments

Conjecture: Given the function f(x,y) = (sqrt(x^2+y) + x)^2 and constant k=f(x,y), then for all integers x >= 1 and y=[+-]1, k may be irrational, but (k^n + k^(-n))/2 always produces integer sequences; y=-1 results shown here; y=1 results are A188645.
Also square array A(n,k), n >= 1, k >= 0, read by antidiagonals, where A(n,k) is Chebyshev polynomial of the first kind T_{2*k}(x), evaluated at x=n. - Seiichi Manyama, Dec 30 2018

Examples

			Row 2 gives {( (2+sqrt(3))^(2*n) + (2-sqrt(3))^(2*n) )/2}.
Square array begins:
     | 0    1       2          3             4
-----+---------------------------------------------
   1 | 1,   1,      1,         1,            1, ...
   2 | 1,   7,     97,      1351,        18817, ...
   3 | 1,  17,    577,     19601,       665857, ...
   4 | 1,  31,   1921,    119071,      7380481, ...
   5 | 1,  49,   4801,    470449,     46099201, ...
   6 | 1,  71,  10081,   1431431,    203253121, ...
   7 | 1,  97,  18817,   3650401,    708158977, ...
   8 | 1, 127,  32257,   8193151,   2081028097, ...
   9 | 1, 161,  51841,  16692641,   5374978561, ...
  10 | 1, 199,  79201,  31521799,  12545596801, ...
  11 | 1, 241, 116161,  55989361,  26986755841, ...
  12 | 1, 287, 164737,  94558751,  54276558337, ...
  13 | 1, 337, 227137, 153090001, 103182433537, ...
  14 | 1, 391, 305761, 239104711, 186979578241, ...
  15 | 1, 449, 403201, 362074049, 325142092801, ...
  ...
		

Crossrefs

Row 2 is A011943, row 3 is A056771, row 8 is A175633, (row 2)*2 is A067902, (row 9)*2 is A089775.
(column 1)*2 is A060626.
Cf. A188645 (f(x, y) as above with y=1).
Diagonals give A173129, A322899.

Programs

  • Mathematica
    max = 9; y = -1; t = Table[k = ((x^2 + y)^(1/2) + x)^2; ((k^n) + (k^(-n)))/2 // FullSimplify, {n, 0, max - 1}, {x, 1, max}]; Table[ t[[n - k + 1, k]], {n, 1, max}, {k, 1, n}] // Flatten (* Jean-François Alcover, Jul 17 2013 *)

Formula

A(n,k) = (A188646(n,k-1) + A188646(n,k))/2.
A(n,k) = Sum_{j=0..k} binomial(2*k,2*j)*(n^2-1)^(k-j)*n^(2*j). - Seiichi Manyama, Jan 01 2019

Extensions

Edited by Seiichi Manyama, Dec 30 2018
More terms from Seiichi Manyama, Jan 01 2019

A101124 Number triangle associated to Chebyshev polynomials of first kind.

Original entry on oeis.org

1, 0, 1, -1, 1, 1, 0, 1, 2, 1, 1, 1, 7, 3, 1, 0, 1, 26, 17, 4, 1, -1, 1, 97, 99, 31, 5, 1, 0, 1, 362, 577, 244, 49, 6, 1, 1, 1, 1351, 3363, 1921, 485, 71, 7, 1, 0, 1, 5042, 19601, 15124, 4801, 846, 97, 8, 1, -1, 1, 18817, 114243, 119071, 47525, 10081, 1351, 127, 9, 1, 0, 1, 70226, 665857, 937444, 470449, 120126, 18817, 2024, 161
Offset: 0

Views

Author

Paul Barry, Dec 02 2004

Keywords

Examples

			As a number triangle, rows begin:
  {1},
  {0,1},
  {-1,1,1},
  {0,1,2,1},
  ...
As a square array, rows begin
   1, 1,  1,   1,    1, ...
   0, 1,  2,   3,    4, ...
  -1, 1,  7,  17,   31, ...
   0, 1, 26,  99,  244, ...
   1, 1, 97, 577, 1921, ...
		

Crossrefs

Row sums are A101125.
Diagonal sums are A101126.
Main diagonal gives A115066.
Mirror of A322836.
Cf. A053120.

Programs

  • Mathematica
    T[n_, k_] := SeriesCoefficient[x^k (1 - k x)/(1 - 2 k x + x^2), {x, 0, n}];
    Table[T[n, k], {n, 0, 11}, {k, 0, n}] // Flatten (* Jean-François Alcover, Jun 12 2017 *)

Formula

Number triangle S(n, k)=T(n-k, k), k
Columns have g.f. x^k(1-kx)/(1-2kx+x^2).
Also, square array if(n=0, 1, T(n, k)) read by antidiagonals.

A323117 a(n) = T_{n}(n-1) where T_{n}(x) is a Chebyshev polynomial of the first kind.

Original entry on oeis.org

1, 0, 1, 26, 577, 15124, 470449, 17057046, 708158977, 33165873224, 1730726404001, 99612037019890, 6269617090376641, 428438743526336412, 31592397706723526737, 2500433598371461203374, 211434761022028192051201, 19023879409608991280267536
Offset: 0

Author

Seiichi Manyama, Jan 05 2019

Keywords

Crossrefs

Programs

  • Mathematica
    Table[ChebyshevT[n, n - 1], {n, 0, 20}] (* Vaclav Kotesovec, Jan 05 2019 *)
  • PARI
    a(n) = polchebyshev(n, 1, n-1);
    
  • PARI
    a(n) = round(cos(n*acos(n-1))); \\ Seiichi Manyama, Mar 05 2021
    
  • PARI
    a(n) = if(n==0, 1, n*sum(k=0, n, (2*n-4)^k*binomial(n+k, 2*k)/(n+k))); \\ Seiichi Manyama, Mar 05 2021

Formula

a(n)^2 - ((n - 1)^2 - 1) * A323118(n-1)^2 = 1 for n > 0.
a(n) = A322836(n,n-1) for n > 0.
a(n) ~ exp(-1) * 2^(n-1) * n^n. - Vaclav Kotesovec, Jan 05 2019
a(n) = cos(n*arccos(n-1)). - Seiichi Manyama, Mar 05 2021
a(n) = n * Sum_{k=0..n} (2*n-4)^k * binomial(n+k,2*k)/(n+k) for n > 0. - Seiichi Manyama, Mar 05 2021

A322888 Chebyshev T-polynomials T_n(16).

Original entry on oeis.org

1, 16, 511, 16336, 522241, 16695376, 533729791, 17062657936, 545471324161, 17438019715216, 557471159562751, 17821639086292816, 569734979601807361, 18213697708171542736, 582268591681887560191, 18614381236112230383376, 595077930963909484707841
Offset: 0

Author

Seiichi Manyama, Dec 29 2018

Keywords

Crossrefs

Column 16 of A322836.

Programs

  • GAP
    a:=[1,16];; for n in [3..20] do a[n]:=32*a[n-1]-a[n-2]; od; Print(a); # Muniru A Asiru, Dec 31 2018
    
  • Magma
    I:=[1, 16]; [n le 2 select I[n] else 32*Self(n-1)-Self(n-2): n in [1..20]]; // Vincenzo Librandi, Jan 02 2019
  • Maple
    seq(coeff(series((1-16*x)/(1-32*x+x^2),x,n+1), x, n), n = 0 .. 20); # Muniru A Asiru, Dec 31 2018
  • Mathematica
    Array[ChebyshevT[#, 16] &, 17, 0] (* or *)
    With[{k = 16}, CoefficientList[Series[(1 - k x)/(1 - 2 k x + x^2), {x, 0, 16}], x]] (* Michael De Vlieger, Jan 01 2019 *)
  • PARI
    {a(n) = polchebyshev(n, 1, 16)}
    
  • PARI
    Vec((1 - 16*x) / (1 - 32*x + x^2) + O(x^20)) \\ Colin Barker, Dec 30 2018
    

Formula

a(0) = 1, a(1) = 16 and a(n) = 32*a(n-1) - a(n-2) for n > 1.
From Colin Barker, Dec 30 2018: (Start)
G.f.: (1 - 16*x) / (1 - 32*x + x^2).
a(n) = ((16+sqrt(255))^(-n) * (1+(16+sqrt(255))^(2*n))) / 2.
(End)

A322889 Chebyshev T-polynomials T_n(18).

Original entry on oeis.org

1, 18, 647, 23274, 837217, 30116538, 1083358151, 38970776898, 1401864610177, 50428155189474, 1814011722210887, 65253993844402458, 2347329766676277601, 84438617606501591178, 3037442904067381004807, 109263505928819214581874
Offset: 0

Author

Seiichi Manyama, Dec 29 2018

Keywords

Crossrefs

Column 18 of A322836.

Programs

  • GAP
    a:=[1,18];; for n in [3..20] do a[n]:=36*a[n-1]-a[n-2]; od; Print(a); # Muniru A Asiru, Dec 31 2018
    
  • Magma
    I:=[1, 18]; [n le 2 select I[n] else 36*Self(n-1)-Self(n-2): n in [1..20]]; // Vincenzo Librandi, Jan 02 2019
  • Maple
    seq(coeff(series((1-18*x)/(1-36*x+x^2),x,n+1), x, n), n = 0 .. 20); # Muniru A Asiru, Dec 31 2018
  • Mathematica
    Array[ChebyshevT[#, 18] &, 16, 0] (* or *)
    With[{k = 18}, CoefficientList[Series[(1 - k x)/(1 - 2 k x + x^2), {x, 0, 15}], x]] (* Michael De Vlieger, Jan 01 2019 *)
  • PARI
    {a(n) = polchebyshev(n, 1, 18)}
    
  • PARI
    Vec((1 - 18*x) / (1 - 36*x + x^2) + O(x^20)) \\ Colin Barker, Dec 30 2018
    

Formula

a(0) = 1, a(1) = 18 and a(n) = 36*a(n-1) - a(n-2) for n > 1.
From Colin Barker, Dec 30 2018: (Start)
G.f.: (1 - 18*x) / (1 - 36*x + x^2).
a(n) = ((18+sqrt(323))^(-n) * (1+(18+sqrt(323))^(2*n))) / 2. (End)
E.g.f.: exp(18*x)*cosh(sqrt(323)*x). - Stefano Spezia, Aug 02 2025

A322890 a(n) = value of Chebyshev T-polynomial T_n(20).

Original entry on oeis.org

1, 20, 799, 31940, 1276801, 51040100, 2040327199, 81562047860, 3260441587201, 130336101440180, 5210183616019999, 208277008539359780, 8325870157958371201, 332826529309795488260, 13304735302233861159199, 531856585560044650879700
Offset: 0

Author

Seiichi Manyama, Dec 29 2018

Keywords

Crossrefs

Column 20 of A322836.
Cf. A041758.

Programs

  • GAP
    a:=[1,20];; for n in [3..20] do a[n]:=40*a[n-1]-a[n-2]; od; Print(a); # Muniru A Asiru, Dec 31 2018
  • Maple
    seq(coeff(series((1-20*x)/(1-40*x+x^2),x,n+1), x, n), n = 0 .. 20); # Muniru A Asiru, Dec 31 2018
  • Mathematica
    CoefficientList[Series[(1 - 20 x)/(1 - 40 x + x^2), {x, 0, 15}], x] (* or *)
    Array[ChebyshevT[#, 20] &, 16, 0] (* Michael De Vlieger, Jan 01 2019 *)
  • PARI
    {a(n) = polchebyshev(n, 1, 20)}
    
  • PARI
    Vec((1 - 20*x) / (1 - 40*x + x^2) + O(x^20)) \\ Colin Barker, Dec 30 2018
    

Formula

a(0) = 1, a(1) = 20 and a(n) = 40*a(n-1) - a(n-2) for n > 1.
From Colin Barker, Dec 30 2018: (Start)
G.f.: (1 - 20*x) / (1 - 40*x + x^2).
a(n) = ((20+sqrt(399))^(-n) * (1+(20+sqrt(399))^(2*n))) / 2.
(End)
Showing 1-9 of 9 results.