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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A061171 One half of second column of Lucas bisection triangle (odd part).

Original entry on oeis.org

3, 19, 79, 283, 940, 2982, 9171, 27581, 81557, 237995, 687158, 1966764, 5588259, 15780103, 44323195, 123920827, 345062176, 957403026, 2647935987, 7302634865, 20087869313, 55128445259, 150971982314
Offset: 0

Views

Author

Wolfdieter Lang, Apr 20 2001

Keywords

Comments

Numerator of g.f. is on half of row polynomial Sum_{m=0..2} A061187(1,m) * x^m.

Crossrefs

Programs

  • Magma
    I:=[3,19,79,283]; [n le 4 select I[n] else 6*Self(n-1) - 11*Self(n-2) + 6*Self(n-3) - Self(n-4): n in [1..30]]; // G. C. Greubel, Dec 21 2017
  • Mathematica
    CoefficientList[Series[(1+x)(3-2x)/(1-3x+x^2)^2,{x,0,30}],x] (* or *) LinearRecurrence[{6,-11,6,-1},{3,19,79,283},30] (* Harvey P. Dale, Oct 11 2012 *)
  • PARI
    my(x='x+O('x^30)); Vec((1+x)*(3-2*x)/(1-3*x+x^2)^2) \\ G. C. Greubel, Dec 21 2017
    

Formula

2*a(n) = A060924(n+1, 1).
G.f.: (1+x)*(3-2*x)/(1-3*x+x^2)^2.
a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3) - a(n-4), with a(0)=3, a(1)=19, a(2)=79, a(3)=283. - Harvey P. Dale, Oct 11 2012
a(n) = Fibonacci(2*n+4) + n*Lucas(2*n+3). - Lechoslaw Ratajczak, May 06 2020

A065034 a(n) = Lucas(2*n) + 1.

Original entry on oeis.org

3, 4, 8, 19, 48, 124, 323, 844, 2208, 5779, 15128, 39604, 103683, 271444, 710648, 1860499, 4870848, 12752044, 33385283, 87403804, 228826128, 599074579, 1568397608, 4106118244, 10749957123, 28143753124, 73681302248, 192900153619, 505019158608, 1322157322204
Offset: 0

Views

Author

N. J. A. Sloane, Nov 04 2001

Keywords

Crossrefs

Cf. A002878 (first differences). - R. J. Mathar, Jul 18 2009

Programs

  • Magma
    [ Lucas(2*n) + 1: n in [0..210]]; // Vincenzo Librandi, Apr 15 2011
  • Maple
    a:= n-> (<<0|1>, <1|1>>^(2*n). <<2,1>>)[1, 1]+1:
    seq(a(n), n=0..30);  # Alois P. Heinz, Nov 01 2016
  • Mathematica
    LucasL[2 Range[30]]+1 (* Harvey P. Dale, Oct 21 2011 *)
    LinearRecurrence[{4, -4, 1}, {3, 4, 8}, 30] (* Jean-François Alcover, Jan 08 2019 *)
  • PARI
    a(n) = { fibonacci(2*n + 1) + fibonacci(2*n - 1) + 1 } \\ Harry J. Smith, Oct 03 2009
    
  • PARI
    Vec((3-2*x)*(1-2*x)/((1-x)*(1-3*x+x^2)) + O(x^40)) \\ Colin Barker, Nov 01 2016
    

Formula

a(n) = F(2*n+1) + F(2*n-1) + 1 = A005248(n) + 1.
From R. J. Mathar, Jul 18 2009: (Start)
a(n) = 4*a(n-1) - 4*a(n-2) + a(n-3).
G.f.: 1/(1-x) + (2-3*x)/(1-3*x+x^2). (End)
a(n) = 1 + ((3-sqrt(5))/2)^n + ((3+sqrt(5))/2)^n. - Colin Barker, Nov 01 2016

Extensions

a(0)=3 prepended by Joerg Arndt, Nov 01 2016

A087799 a(n) = 10*a(n-1) - a(n-2), starting with a(0) = 2 and a(1) = 10.

Original entry on oeis.org

2, 10, 98, 970, 9602, 95050, 940898, 9313930, 92198402, 912670090, 9034502498, 89432354890, 885289046402, 8763458109130, 86749292044898, 858729462339850, 8500545331353602, 84146723851196170, 832966693180608098, 8245520207954884810
Offset: 0

Views

Author

Nikolay V. Kosinov (kosinov(AT)unitron.com.ua), Oct 11 2003

Keywords

Comments

a(n+1)/a(n) converges to (5+sqrt(24)) = 9.8989794... a(0)/a(1)=2/10; a(1)/a(2)=10/98; a(2)/a(3)=98/970; a(3)/a(4)=970/9602; ... etc. Lim a(n)/a(n+1) as n approaches infinity = 0.10102051... = 1/(5+sqrt(24)) = (5-sqrt(24)).
Except for the first term, positive values of x (or y) satisfying x^2 - 10xy + y^2 + 96 = 0. - Colin Barker, Feb 25 2014
A triangle whose sides are a(n) - 1, a(n) and a(n) + 1 is nearly Fleenor-Heronian since its area is the product of an integer and the square root of 2. See A003500. - Charlie Marion, Dec 18 2020

Examples

			a(4) = 9602 = 10*a(3) - a(2) = 10*970 - 98 = (5+sqrt(24))^4 + (5-sqrt(24))^4.
		

Crossrefs

Programs

  • Magma
    I:=[2,10]; [n le 2 select I[n] else 10*Self(n-1) - Self(n-2): n in [1..30]]; // G. C. Greubel, Nov 07 2018
  • Mathematica
    a[0] = 2; a[1] = 10; a[n_] := 10a[n - 1] - a[n - 2]; Table[ a[n], {n, 0, 17}] (* Robert G. Wilson v, Jan 30 2004 *)
    LinearRecurrence[{10,-1}, {2,10}, 30] (* G. C. Greubel, Nov 07 2018 *)
  • PARI
    polsym(x^2 - 10*x + 1,20) \\ Charles R Greathouse IV, Jun 11 2011
    
  • PARI
    {a(n) = 2 * real( (5 + 2 * quadgen(24))^n )}; /* Michael Somos, Feb 25 2014 */
    
  • Sage
    [lucas_number2(n,10,1) for n in range(27)] # Zerinvary Lajos, Jun 25 2008
    

Formula

a(n) = (5+sqrt(24))^n + (5-sqrt(24))^n.
G.f.: (2-10*x)/(1-10*x+x^2). - Philippe Deléham, Nov 02 2008
From Peter Bala, Jan 06 2013: (Start)
Let F(x) = Product_{n = 0..inf} (1 + x^(4*n+1))/(1 + x^(4*n+3)). Let alpha = 5 - sqrt(24). This sequence gives the simple continued fraction expansion of 1 + F(alpha) = 2.09989 80642 72052 68138 ... = 2 + 1/(10 + 1/(98 + 1/(970 + ...))).
Also F(-alpha) = 0.89989 78538 78393 34715 ... has the continued fraction representation 1 - 1/(10 - 1/(98 - 1/(970 - ...))) and the simple continued fraction expansion 1/(1 + 1/((10-2) + 1/(1 + 1/((98-2) + 1/(1 + 1/((970-2) + 1/(1 + ...))))))).
F(alpha)*F(-alpha) has the simple continued fraction expansion 1/(1 + 1/((10^2-4) + 1/(1 + 1/((98^2-4) + 1/(1 + 1/((970^2-4) + 1/(1 + ...))))))). Cf. A174503 and A005248. (End)
a(-n) = a(n). - Michael Somos, Feb 25 2014
From Peter Bala, Oct 16 2019: (Start)
8*Sum_{n >= 1} 1/(a(n) - 12/a(n)) = 1.
12*Sum_{n >= 1} (-1)^(n+1)/(a(n) + 8/a(n)) = 1.
Series acceleration formulas for sums of reciprocals:
Sum_{n >= 1} 1/a(n) = 1/8 - 12*Sum_{n >= 1} 1/(a(n)*(a(n)^2 - 12)) and
Sum_{n >= 1} (-1)^(n+1)/a(n) = 1/12 + 8*Sum_{n >= 1} (-1)^(n+1)/(a(n)*(a(n)^2 + 8)).
Sum_{n >= 1} 1/a(n) = ( (theta_3(5-sqrt(24)))^2 - 1 )/4 and
Sum_{n >= 1} (-1)^(n+1)/a(n) = ( 1 - (theta_3(sqrt(24)-5))^2 )/4, where theta_3(x) = 1 + 2*Sum_{n >= 1} x^(n^2) (see A000122). Cf. A153415 and A003499. (End)
E.g.f.: 2*exp(5*x)*cosh(2*sqrt(6)*x). - Stefano Spezia, Oct 18 2019
From Peter Bala, Mar 29 2022: (Start)
a(n) = 2*T(n,5), where T(n,x) denotes the n-th Chebyshev polynomial of the first kind.
a(2^n) = A135927(n+1) and a(3^n) = A006242(n+1), both for n >= 0. (End)

Extensions

More terms from Colin Barker, Feb 25 2014

A173027 Numbers of rows R of the Wythoff array such that R is the n-th multiple of a tail of the Fibonacci sequence.

Original entry on oeis.org

1, 3, 4, 5, 16, 19, 22, 25, 28, 31, 34, 97, 105, 113, 121, 129, 137, 145, 153, 161, 169, 177, 185, 193, 201, 209, 217, 225, 233, 631, 652, 673, 694, 715, 736, 757, 778, 799, 820, 841, 862, 883, 904, 925, 946, 967, 988, 1009, 1030, 1051, 1072, 1093, 1114, 1135
Offset: 1

Views

Author

Clark Kimberling, Feb 07 2010

Keywords

Comments

Row 1 of the array A173028.
Contribution from K. G. Stier, Dec 08 2012: (Start)
It appears that the numbers of this sequence form groups of m members respectively with same distance d of two consecutive values a(n) such that d is equal to even-indexed Fibonacci numbers (A001906) while m is equal to even-indexed Lucas numbers (A005248). Example: from n=1365 to 3571 d=987 and m=2207;
Also of interest are the gaps between two consecutive groups which appear to be sums of Fibonacci numbers F(2*n) plus F(4*n-2). Example: gap 5 after a(76) is 2639 = F(10) + F(18) = 55 + 2584.
Likewise, the tail (as mentioned in this sequence's name) of the Fibonacci sequence is chopped off by two initial terms at each of the gap positions. (End)

Examples

			Referring to rows of the Wythoff array (A035513),
Row 1: (1,2,3,5,...) = 1*(1,2,3,...)
Row 3: (6,10,16,...) = 2*(3,5,8,...)
Row 4: (9,15,24,...) = 3*(3,5,8,...)
Row 5: (12,20,32,...) = 4*(3,5,8,...)
Row 16: (40,65,105...) = 8*(5,13,21,...).
		

Crossrefs

A198636 One half of total number of round trips, each of length 2n, on the graph P_6 (o-o-o-o-o-o).

Original entry on oeis.org

3, 5, 13, 38, 117, 370, 1186, 3827, 12389, 40169, 130338, 423065, 1373466, 4459278, 14478659, 47011093, 152642789, 495626046, 1609284589, 5225309458, 16966465802, 55089756851, 178875298901, 580804419201, 1885860059450, 6123349080945
Offset: 0

Views

Author

Wolfdieter Lang, Nov 03 2011

Keywords

Comments

See the array and triangle A198632 for the general graph P_N case (there N is n and the length is l=2*k).

Examples

			With the graph P_6 as 1-2-3-4-5-6:
n=0: a(0)=3 because w(6,0)=6, the number of vertices.
n=2: a(2)=5 because the 10 round trips of length 2 are 121, 212, 232, 323, 343, 434, 454, 545, 565 and 656.
		

Crossrefs

Programs

  • Mathematica
    Table[7 (Binomial[2 n - 1, n - 1] + Sum[Binomial[2 n, n - 7 k], {k, Floor[n/7]}]) - 2^(2 n - 1) - (7/2) Boole[n == 0], {n, 0, 25}] (* Michael De Vlieger, Jul 17 2017 *)
  • PARI
    vec_A198636(Nmax)=Vec((3-10*x+6*x^2)/(1-5*x+6*x^2-x^3)+O(x^Nmax)) \\ Indices will start at 1 in this vector. - M. F. Hasler, Nov 03 2013
    
  • PARI
    {a(n) = if( n<0, n=-n; polcoeff( (3 - 12*x + 5*x^2) / (1 - 6*x + 5*x^2 - x^3) + x * O(x^n), n), polcoeff( (3 - 10*x + 6*x^2) / (1 - 5*x + 6*x^2 -x^3) + x * O(x^n), n))}; /* Michael Somos, Jul 17 2017 */

Formula

a(n) = w(6,2*n)/2, n>=0, with w(6,l) the total number of closed walks on the graph P_6 (the simple path with 6 points (vertices) and 5 lines (or edges)).
O.g.f. for w(6,l) (with zeros for odd l): y*(d/dy)S(6,y)/S(6,y) with y=1/x and Chebyshev S-polynomials (coefficients A049310). See also A198632 for a rewritten form.
O.g.f.: (3-10*x+6*x^2)/(1-5*x+6*x^2-x^3). - Colin Barker, Jan 02 2012
Conjecture: a(n) = 2^(2*n)*(sum_{k=1,2,3} (cos(k*Pi/7))^(2*n)). - L. Edson Jeffery, Jan 21 2012 (in fact this conjecture was recently proved in [Barbero, et al.])
a(n) = 7*(binomial(2n-1,n-1) + sum_{k = 1..floor(n/7)} binomial(2n,n-7k)) - 2^(2n-1). - M. Lawrence Glasser, Feb 20 2013
Let r,s,t be the roots of x^3 + x^2 - 2x - 1; then apparently a(n) = r^(2n) + s^(2n) + t^(2n). - James R. Buddenhagen, Nov 03 2013 [This is equivalent to the conjecture by L. Edson Jeffery.]
a(n) = 5*a(n-1) - 6*a(n-2) + a(n-3). - M. F. Hasler, Nov 05 2013
G.f.: F(x) = (sum_{r=0..2} ((3-r)*(-1)^r*binomial(6-r,r))*x^r)/(sum_{s=0..3} ((-1)^s*binomial(6-s,s))*x^s). - L. Edson Jeffery, Nov 23 2013

A237132 Values of x in the solutions to x^2 - 3xy + y^2 + 11 = 0, where 0 < x < y.

Original entry on oeis.org

3, 4, 5, 9, 12, 23, 31, 60, 81, 157, 212, 411, 555, 1076, 1453, 2817, 3804, 7375, 9959, 19308, 26073, 50549, 68260, 132339, 178707, 346468, 467861, 907065, 1224876, 2374727, 3206767, 6217116, 8395425, 16276621, 21979508, 42612747, 57543099, 111561620
Offset: 1

Views

Author

Colin Barker, Feb 04 2014

Keywords

Comments

The corresponding values of y are given by a(n+2).
Positive values of x (or y) satisfying x^2 - 18xy + y^2 + 704 = 0.

Examples

			9 is in the sequence because (x, y) = (9, 23) is a solution to x^2 - 3xy + y^2 + 11 = 0.
		

Crossrefs

Programs

  • PARI
    Vec(-x*(x-1)*(3*x^2+7*x+3)/((x^2-x-1)*(x^2+x-1)) + O(x^100))

Formula

a(n) = 3*a(n-2)-a(n-4).
G.f.: -x*(x-1)*(3*x^2+7*x+3) / ((x^2-x-1)*(x^2+x-1)).
a(n) = F(n+2) + (-1)^n*F(n-3), n>1, with F the Fibonacci numbers (A000045). - Ralf Stephan, Feb 05 2014
Let h(n) = hypergeom([(1 - n)/2, n mod 2 - n/2], [1 - n], -4) then a(n) = h(n-1) + h(n) for n > 3. - Peter Luschny, Sep 03 2019

A047946 a(n) = 5*F(n)^2 + 3*(-1)^n where F(n) are the Fibonacci numbers A000045.

Original entry on oeis.org

3, 2, 8, 17, 48, 122, 323, 842, 2208, 5777, 15128, 39602, 103683, 271442, 710648, 1860497, 4870848, 12752042, 33385283, 87403802, 228826128, 599074577, 1568397608, 4106118242, 10749957123, 28143753122, 73681302248, 192900153617, 505019158608, 1322157322202
Offset: 0

Views

Author

John W. Layman, May 21 1999

Keywords

Comments

Form the matrix A=[1,1,1;2,1,0;1,0,0]. a(n)=trace(A^n). - Paul Barry, Sep 22 2004
The set of prime divisors of elements of this sequence with the exception of 3 is the set of primes that do not divide odd Fibonacci numbers. - Tanya Khovanova, May 19 2008
If a(n) is prime then n is a power of 3 (Boase, 1998). The only values of k not exceeding 12 for which a(3^k) is prime are 0 and 1. - Amiram Eldar, Jun 19 2022

Crossrefs

Second row of array A028412.
Cf. A133247 (prime numbers p such that no odd Fibonacci number is divisible by p).

Programs

  • Mathematica
    Table[LucasL[n]^2 - (-1)^n, {n, 0, 30}] (* Amiram Eldar, Feb 02 2022 *)
  • PARI
    a(n)=5*fibonacci(n)^2+3*(-1)^n
    
  • Python
    from sympy import fibonacci
    def A047946(n): return 5*fibonacci(n)**2+(-3 if n&1 else 3) # Chai Wah Wu, Jul 29 2022

Formula

a(n) = F(3n)/F(n), n>0.
a(n) = 2*a(n-1)+2*a(n-2)-a(n-3).
a(n) = 3a(n-1)-a(n-2)+5(-1)^n.
a(n) = A005248(n) + (-1)^n.
G.f.: ( 3-4*x-2*x^2 ) / ( (1+x)*(x^2-3*x+1) ).
for n>0 a(n) = A000045(3n)/A000045(n) - Benoit Cloitre, Aug 30 2003
For n>0, the linear recurrence for the sequence F(n*k)^2 has signature (a(n),a(n),-1) for n odd, and (a(n),-a(n), 1) for n even. For example, the linear recurrence for the sequence F(3*k)^2 has signature (17, 17, -1) (conjectured). - Greg Dresden, Aug 30 2021
a(n) = Lucas(n)^2 - (-1)^n. - Amiram Eldar, Feb 02 2022

Extensions

Entry improved by comments from Michael Somos.

A104626 Numbers having three 1's in their base-phi representation.

Original entry on oeis.org

4, 5, 6, 8, 19, 48, 124, 323, 844, 2208, 5779, 15128, 39604, 103683, 271444, 710648, 1860499, 4870848, 12752044, 33385283, 87403804, 228826128, 599074579, 1568397608, 4106118244, 10749957123, 28143753124, 73681302248
Offset: 1

Views

Author

Eric W. Weisstein, Mar 17 2005

Keywords

Crossrefs

Programs

  • Magma
    [4,5,6] cat [1 + Fibonacci(2*n-3) + Fibonacci(2*n-5): n in [4..50]]; // G. C. Greubel, Aug 13 2018
  • Mathematica
    Join[{4, 5, 6}, Table[LucasL[2*n-4] + 1, {n, 4, 50}]] (* G. C. Greubel, Aug 13 2018 *)
  • PARI
    for(n=1,50, print1(if(n==1,4, if(n==2, 5, if(n==3, 6, 1 + fibonacci(2*n-3) + fibonacci(2*n-5)))), ", ")) \\ G. C. Greubel, Aug 13 2018
    

Formula

{n: A055778(n) = 3}. - R. J. Mathar, Sep 05 2010
a(n) = Lucas(2*n-4) + 1, for n>3. - Ralf Stephan, Nov 13 2010

Extensions

Terms 5 and 6 added by Jaroslav Krizek, May 25 2010
Edited by R. J. Mathar, Sep 05 2010

A104627 Numbers having 4 1's in their base-phi representation.

Original entry on oeis.org

9, 10, 12, 13, 14, 16, 17, 20, 21, 25, 36, 49, 50, 54, 65, 94, 125, 126, 130, 141, 170, 246, 324, 325, 329, 340, 369, 445, 644, 845, 846, 850, 861, 890, 966, 1165, 1686, 2209, 2210, 2214, 2225, 2254, 2330, 2529, 3050, 4414
Offset: 1

Views

Author

Eric W. Weisstein, Mar 17 2005

Keywords

Crossrefs

Programs

  • Mathematica
    q[n_] := Plus @@ RealDigits[n, GoldenRatio, 2*Ceiling[ Log[GoldenRatio, n]] ][[1]] == 4; Select[Range[4500], q] (* Amiram Eldar, Jan 20 2022 *)

Formula

There is a 24-state automaton accepting exactly the Zeckendorf representation of members of this sequence. - Jeffrey Shallit, May 03 2023

A104628 Numbers having 5 1's in their base-phi representation.

Original entry on oeis.org

11, 15, 22, 23, 24, 26, 30, 31, 32, 34, 35, 37, 41, 42, 43, 45, 46, 51, 52, 53, 55, 66, 83, 95, 112, 127, 128, 129, 131, 142, 171, 217, 247, 293, 326, 327, 328, 330, 341, 370, 446, 568, 645, 767, 847, 848, 849, 851, 862, 891, 967, 1166, 1487, 1687, 2008, 2211
Offset: 1

Views

Author

Eric W. Weisstein, Mar 17 2005

Keywords

Crossrefs

Programs

  • Mathematica
    q[n_] := Plus @@ RealDigits[n, GoldenRatio, 2*Ceiling[ Log[GoldenRatio, n]] ][[1]] == 5; Select[Range[2000], q] (* Amiram Eldar, Jan 20 2022 *)

Formula

There is a 46-state automaton accepting precisely the Zeckendorf representation of members of this sequence. - Jeffrey Shallit, May 03 2023
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