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 30 results.

A105579 a(n+3) = 2a(n+2) - 3a(n+1) + 2a(n); a(0) = 1, a(1) = 3, a(2) = 4.

Original entry on oeis.org

1, 3, 4, 1, -4, -3, 8, 17, 4, -27, -32, 25, 92, 45, -136, -223, 52, 501, 400, -599, -1396, -195, 2600, 2993, -2204, -8187, -3776, 12601, 20156, -5043, -45352, -35263, 55444, 125973, 15088, -236855, -267028, 206685, 740744, 327377, -1154108, -1808859, 499360, 4117081, 3118364, -5115795, -11352520
Offset: 0

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Author

Creighton Dement, Apr 14 2005

Keywords

Comments

Floretion Algebra Multiplication Program, FAMP Code: famseq[.5'j + .5'k + .5j' + .5k' + .5'ii' + .5e]

Crossrefs

Cf. Equals (1/2) [A107920(n+4) - 2*A107920(n-1) + 3 ].

Programs

  • Mathematica
    Table[(3 - ((1-I*Sqrt[7])^n + (1+I*Sqrt[7])^n)/2^n)/2 // Simplify, {n, 1, 50}] (* Jean-François Alcover, Jun 04 2017 *)

Formula

a(n+1) - a(n) = A002249(n).
a(n) = 2*a(n-1)-3*a(n-2)+2*a(n-3). G.f.: (1+x+x^2)/((1-x)*(1-x+2*x^2)). [Colin Barker, Mar 27 2012]

Extensions

Corrected by T. D. Noe, Nov 07 2006

A146084 Expansion of 1/(1-x(1-12x)).

Original entry on oeis.org

1, 1, -11, -23, 109, 385, -923, -5543, 5533, 72049, 5653, -858935, -926771, 9380449, 20501701, -92063687, -338084099, 766680145, 4823689333, -4376472407, -62260744403, -9743075519, 737385857317, 854302763545, -7994327524259
Offset: 0

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Author

Philippe Deléham, Oct 27 2008

Keywords

Comments

Row sums of Riordan array (1,x(1-12x)).

Crossrefs

Programs

Formula

a(n) = a(n-1)-12*a(n-2), a(0)=1, a(1)=1.
a(n) = Sum_{k, 0<=k<=n} A109466(n,k)*12^(n-k).

A128100 Triangle read by rows: T(n,k) is the number of ways to tile a 2 X n rectangle with k pieces of 2 X 2 tiles and n-2k pieces of 1 X 2 tiles (0 <= k <= floor(n/2)).

Original entry on oeis.org

1, 1, 2, 1, 3, 2, 5, 5, 1, 8, 10, 3, 13, 20, 9, 1, 21, 38, 22, 4, 34, 71, 51, 14, 1, 55, 130, 111, 40, 5, 89, 235, 233, 105, 20, 1, 144, 420, 474, 256, 65, 6, 233, 744, 942, 594, 190, 27, 1, 377, 1308, 1836, 1324, 511, 98, 7, 610, 2285, 3522, 2860, 1295, 315, 35, 1, 987, 3970
Offset: 0

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Author

Emeric Deutsch, Feb 18 2007

Keywords

Comments

Row sums are the Jacobsthal numbers (A001045). Column 0 yields the Fibonacci numbers (A000045); the other columns yield convolved Fibonacci numbers (A001629, A001628, A001872, A001873, etc.). Sum_{k=0..floor(n/2)} k*T(n,k) = A073371(n-2).
Triangle T(n,k), with zeros omitted, given by (1, 1, -1, 0, 0, 0, 0, 0, 0, 0, ...) DELTA (0, 1, -1, 0, 0, 0, 0, 0, 0, 0, ...) where DELTA is the operator defined in A084938. - Philippe Deléham, Jan 24 2012
Riordan array (1/(1-x-x^2), x^2/(1-x-x^2)), with zeros omitted. - Philippe Deléham, Feb 06 2012
Diagonal sums are A000073(n+2) (tribonacci numbers). - Philippe Deléham, Feb 16 2014
Number of induced subgraphs of the Fibonacci cube Gamma(n-1) that are isomorphic to the hypercube Q_k. Example: row n=4 is 5, 5, 1; indeed, the Fibonacci cube Gamma(3) is a square with an additional pendant edge attached to one of its vertices; it has 5 vertices (i.e., Q_0's), 5 edges (i.e., Q_1's) and 1 square (i.e., Q_2). - Emeric Deutsch, Aug 12 2014
Row n gives the coefficients of the polynomial p(n,x) defined as the numerator of the rational function given by f(n,x) = 1 + (x + 1)/f(n-1,x), where f(x,0) = 1. Conjecture: for n > 2, p(n,x) is irreducible if and only if n is a (prime - 2). - Clark Kimberling, Oct 22 2014

Examples

			Triangle starts:
   1;
   1;
   2,  1;
   3,  2;
   5,  5,  1;
   8, 10,  3;
  13, 20,  9,  1;
  21, 38, 22,  4;
From _Philippe Deléham_, Jan 24 2012: (Start)
Triangle (1, 1, -1, 0, 0, ...) DELTA (0, 1, -1, 0, 0, 0, ...) begins:
   1;
   1,  0;
   2,  1,  0;
   3,  2,  0,  0;
   5,  5,  1,  0,  0;
   8, 10,  3,  0,  0,  0;
  13, 20,  9,  1,  0,  0,  0;
  21, 38, 22,  4,  0,  0,  0,  0; (End)
From _Clark Kimberling_, Oct 22 2014: (Start)
Here are the first 4 polynomials p(n,x) as in Comment and generated by Mathematica program:
  1
  2 +  x
  3 + 2x
  5 + 5x + x^2. (End)
		

Crossrefs

Programs

  • Maple
    G:=1/(1-z-(1+t)*z^2): Gser:=simplify(series(G,z=0,19)): for n from 0 to 16 do P[n]:=sort(coeff(Gser,z,n)) od: for n from 0 to 16 do seq(coeff(P[n],t,j),j=0..floor(n/2)) od; # yields sequence in triangular form
  • Mathematica
    p[x_, n_] := 1 + (x + 1)/p[x, n - 1]; p[x_, 1] = 1;
    Numerator[Table[Factor[p[x, n]], {n, 1, 20}]]  (* Clark Kimberling, Oct 22 2014 *)

Formula

G.f.: 1/(1-z-(1+t)z^2).
Sum_{k=0..n} T(n,k)*x^k = A053404(n), A015447(n), A015446(n), A015445(n), A015443(n), A015442(n), A015441(n), A015440(n), A006131(n), A006130(n), A001045(n+1), A000045(n+1), A000012(n), A010892(n), A107920(n+1), A106852(n), A106853(n), A106854(n), A145934(n), A145976(n), A145978(n), A146078(n), A146080(n), A146083(n), A146084(n) for x = 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, and -13, respectively. - Philippe Deléham, Jan 24 2012
T(n,k) = T(n-1,k) + T(n-2,k) + T(n-2,k-1). - Philippe Deléham, Jan 24 2012
G.f.: T(0)/2, where T(k) = 1 + 1/(1 - (2*k+1+ x*(1+y))*x/((2*k+2+ x*(1+y))*x + 1/T(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Nov 06 2013
T(n,k) = Sum_{i=k..floor(n/2)} binomial(n-i,i)*binomial(i,k). See Corollary 3.3 in the Klavzar et al. link. - Emeric Deutsch, Aug 12 2014

A192395 a(n) = 2*a(n-1) - 2*a(n-2) + a(n-3) + 2*a(n-4) starting with a(0..3) = 0, 0, 0, 1.

Original entry on oeis.org

0, 0, 0, 1, 2, 2, 1, 2, 8, 17, 22, 22, 33, 78, 156, 233, 298, 442, 833, 1546, 2464, 3553, 5390, 9230, 16161, 26358, 40404, 62713, 103298, 174290, 285505, 451154, 712184, 1156145, 1910086, 3122374, 5005089, 7987806, 12907980, 21090185, 34362394, 55428010
Offset: 0

Views

Author

Paul Curtz, Jun 29 2011

Keywords

Crossrefs

Programs

  • Magma
    I:=[0,0,0,1]; [n le 4 select I[n] else 2*Self(n-1)-2*Self(n-2)+Self(n-3)+2*Self(n-4): n in [1..50]]; // Vincenzo Librandi, Nov 25 2011
    
  • Maple
    a:= n-> (<<0|1|0|0>, <0|0|1|0>, <0|0|0|1>, <2|1|-2|2>>^n)[1,4]:
    seq(a(n), n=0..45);  # Alois P. Heinz, Jul 11 2023
  • Mathematica
    LinearRecurrence[{2,-2,1,2},{0,0,0,1},100] (* Vincenzo Librandi, Nov 25 2011 *)
  • SageMath
    @CachedFunction
    def a(n): # a = A192395
        if (n<4): return n//3
        else: return 2*a(n-1) - 2*a(n-2) + a(n-3) + 2*a(n-4)
    [a(n) for n in range(51)] # G. C. Greubel, Jul 10 2023

Formula

From R. J. Mathar, Jul 14 2011: (Start)
G.f.: x^3/((1-x+2*x^2)*(1-x-x^2)).
a(n) = (A000045(n) - A107920(n))/3. (End)

A340670 Number of complex base i-1 points which can be represented within n bits and negated within those n bits.

Original entry on oeis.org

1, 1, 1, 3, 5, 15, 29, 47, 101, 199, 413, 847, 1621, 3255, 6541, 13087, 26373, 52423, 104637, 209711, 419253, 839511, 1678317, 3353919, 6710629, 13421287, 26845213, 53693007, 107366933, 214742391, 429498701, 858994271, 1718023109, 3435955975, 6871883645
Offset: 0

Views

Author

Kevin Ryde, Jan 15 2021

Keywords

Comments

Complex base i-1 of Khmelnik and Penney uses an integer m to represent a complex integer point z(m) = A318438(m) + A318439(m)*i. A340669(m) is the negation of z in this representation. a(n) is how many n-bit m are negatable within those n bits, i.e., how many m in the range 0 <= m < 2^n have also 0 <= A340669(m) < 2^n.
A geometric interpretation of a(n) is to draw a unit square around each point z(0) to z(2^n-1), rotate a copy by 180 degrees about the origin, and measure its area of intersection with the original.
The bit-flip rule in A340669 gives the recurrence formula below. A low 0-bit of m has a(n-1) negatables above it, or low 11 is one arbitrary bit then negatables above so 2*a(n-3), or low 01 is three arbitrary so 8*a(n-5). This can be thought of the number of compositions of n (partitions with order) into parts 1,3,5 with 2 types of part 3 and 8 types of part 5.

Examples

			For n=3, the a(3)=3 points of n bits are m = 0,3,7 < 2^n, which negate to A340669(0,3,7) = 0,7,3 < 2^n.  These m are located at z = 0,i,-i,
               negate        intersection
  z(0..7)    (rotate 180)   a(3) = 3 points
                * *
   * *            * *             *
     o *        * o               o
   * *            * *             *
     * *
		

Crossrefs

Programs

  • PARI
    { my(table=[4,-2,-2,6, -4,2,2,-6], p=Mod('x,2-'x+'x^2));
    a(n) = (6<
    				

Formula

a(n) = a(n-1) + 2*a(n-3) + 8*a(n-5).
a(n) = (2/5)*2^n + (h/15)*2^floor(n/2) + (2/3)*Im((1/2 + i*sqrt(7)/2)^(n+1)) where h = 4,-2,-2,6, -4,2,2,-6 according as n == 0 to 7 (mod 8) respectively.
a(n) = (2/5)*2^n + (1/3)*A107920(n+1) + (1/15)*A078069(n+2).
G.f.: 1/(1 - x - 2*x^3 - 8*x^5).
G.f.: (2/5)/(1-2*x) + (1/3)/(1-x+2*x^2) + (2/15)*(2+3*x)/(1+2*x+2*x^2).

A332332 Coefficients of L-series for elliptic curve "33a1": y^2 + x*y = x^3 + x^2 - 11*x.

Original entry on oeis.org

1, 1, -1, -1, -2, -1, 4, -3, 1, -2, 1, 1, -2, 4, 2, -1, -2, 1, 0, 2, -4, 1, 8, 3, -1, -2, -1, -4, -6, 2, -8, 5, -1, -2, -8, -1, 6, 0, 2, 6, -2, -4, 0, -1, -2, 8, 8, 1, 9, -1, 2, 2, 6, -1, -2, -12, 0, -6, -4, -2, 6, -8, 4, 7, 4, -1, -4, 2, -8, -8, 0, -3, -14, 6
Offset: 1

Views

Author

Michael Somos, Feb 23 2020

Keywords

Examples

			G.f. = x + x^2 - x^3 - x^4 - 2*x^5 - x^6 + 4*x^7 - 3*x^8 + x^9 + ...
		

Crossrefs

Programs

  • Magma
    A := Basis( ModularForms( Gamma0(33), 2), 75); A[2] + A[3] - A[4] - A[5] - A[6];
    
  • PARI
    {a(n) = if( n<1, 0, ellak( ellinit( [1, 1, 0, -11, 0], 1), n))};
    
  • PARI
    {a(n) = my(A, t1, t3); if( n<1, 0, n--; A = x * O(x^n); t1 = eta(x + A) * eta(x^11 + A); t3 = x * eta(x^3 + A) * eta(x^33 + A); polcoeff( t1^2 + 3*t1*t3 + 3*t3^2, n))};
    
  • Sage
    def a(n):
        return EllipticCurve("33a1").an(n)  # Robin Visser, Sep 30 2023

Formula

Expansion of eta(q)^2*eta(q^11)^2 + 3*eta(q)*eta(q^3)*eta(q^11)*eta(q^33) + 3*eta(q^3)^2*eta(q^33)^2 in powers of q.
G.f. is a period 1 Fourier series which satisfies f(-1 / (33 t)) = 33 (t/i)^2 f(t) where q = exp(2 Pi i t).
a(n) is multiplicative with a(3^n) = (-1)^n, a(11^n) = 1. a(2^n) = A107920(n+1). a(7^n) = A168175(n).

A077876 Expansion of (1-x)^(-1)/(1-x+2*x^2).

Original entry on oeis.org

1, 2, 1, -2, -3, 2, 9, 6, -11, -22, 1, 46, 45, -46, -135, -42, 229, 314, -143, -770, -483, 1058, 2025, -90, -4139, -3958, 4321, 12238, 3597, -20878, -28071, 13686, 69829, 42458, -97199, -182114, 12285, 376514, 351945, -401082, -1104971, -302806, 1907137, 2512750, -1301523, -6327022
Offset: 0

Views

Author

N. J. A. Sloane, Nov 17 2002

Keywords

Comments

Row sums of Riordan array (1/(1-x),x(1-2x)). - Paul Barry, Jul 18 2005

Crossrefs

Programs

Formula

a(n) = Sum_{k=0..n} U(k, 1/(2*sqrt(2)))*sqrt(2)^k. - Paul Barry, Nov 20 2003 [There is a missing parenthesis, but it is not clear where it should be inserted. - N. J. A. Sloane, Feb 08 2015] [corrected by Jason Yuen, Aug 22 2024]
a(n) = Sum_{k=2..n-2} A107920(k). - R. J. Mathar, Oct 13 2017
a(n) = Sum_{k=0..floor((n+1)/2)} binomial(n+1-k,k+1)*(-2)^k, n>=0. - Taras Goy, Apr 15 2020

A105576 a(n) = 2*a(n-1) - 3*a(n-2) + 2*a(n-3) with a(0) = 3, a(1) = 4, a(2) = 0.

Original entry on oeis.org

3, 4, 0, -6, -4, 10, 20, 2, -36, -38, 36, 114, 44, -182, -268, 98, 636, 442, -828, -1710, -52, 3370, 3476, -3262, -10212, -3686, 16740, 24114, -9364, -57590, -38860, 76322, 154044, 1402, -306684, -309486, 303884, 922858, 315092, -1530622, -2160804, 900442, 5222052, 3421170
Offset: 0

Views

Author

Creighton Dement, Apr 14 2005

Keywords

Comments

Floretion Algebra Multiplication Program, FAMP Code: 1vesseq[.5'j + .5'k + .5j' + .5k' + .5'ii' + .5e]

Crossrefs

Equals 2*A107920(n) + A107920(n-1) + 1.

Programs

  • Mathematica
    LinearRecurrence[{2,-3,2},{3,4,0},50] (* Harvey P. Dale, Jul 05 2022 *)

Formula

2*a(n) = A105225(n) + A105577(n) + 4*((-1)^n)*A001607(n+1)
G.f.: (3-2x+x^2)/((1-x)(1-x+2x^2)). a(n)=1+A107920(n)+2*A107920(n+1). [From R. J. Mathar, Feb 04 2009]

A191897 Coefficients of the Z(n,x) polynomials; Z(0,x) = 1, Z(1,x) = x and Z(n,x) = x*Z(n-1,x) - 2*Z(n-2,x), n >= 2.

Original entry on oeis.org

1, 1, 0, 1, 0, -2, 1, 0, -4, 0, 1, 0, -6, 0, 4, 1, 0, -8, 0, 12, 0, 1, 0, -10, 0, 24, 0, -8, 1, 0, -12, 0, 40, 0, -32, 0, 1, 0, -14, 0, 60, 0, -80, 0, 16, 1, 0, -16, 0, 84, 0, -160, 0, 80, 0, 1, 0, -18, 0, 112, 0, -280, 0, 240, 0, -32
Offset: 0

Views

Author

Paul Curtz, Jun 19 2011

Keywords

Comments

The coefficients of the Z(n,x) polynomials by decreasing exponents, see the formulas, define this triangle.

Examples

			The first few rows of the coefficients of the Z(n,x) are
  1;
  1,    0;
  1,    0,   -2;
  1,    0,   -4,    0;
  1,    0,   -6,    0,    4;
  1,    0,   -8,    0,   12,    0;
  1,    0,  -10,    0,   24,    0,   -8;
  1,    0,  -12,    0,   40,    0,  -32,    0;
  1,    0,  -14,    0,   60,    0,  -80,    0,   16;
  1,    0,  -16,    0,   84,    0, -160,    0,   80,    0;
		

Crossrefs

Row sums: A107920(n+1). Main diagonal: A077966(n).
Z(n,x=1) = A107920(n+1), Z(n,x=2) = A009545(n+1),
Z(n,x=3) = A000225(n+1), Z(n,x=4) = A007070(n),
Z(n,x=5) = A107839(n), Z(n,x=6) = A154244(n),
Z(n,x=7) = A186446(n), Z(n,x=8) = A190975(n+1),
Z(n,x=9) = A190979(n+1), Z(n,x=10) = A190869(n+1).
Row sum without sign: A113405(n+1).

Programs

  • Maple
    nmax:=10: Z(0, x):=1 : Z(1, x):=x: for n from 2 to nmax do Z(n, x) := x*Z(n-1, x) - 2*Z(n-2, x) od: for n from 0 to nmax do for k from 0 to n do T(n, k) := coeff(Z(n, x), x, n-k) od: od: seq(seq(T(n, k), k=0..n), n=0..nmax); # Johannes W. Meijer, Jun 27 2011, revised Nov 29 2012
  • Mathematica
    a[n_, k_] := If[OddQ[k], 0, 2^(k/2)*Coefficient[ ChebyshevU[n, x/2], x, n-k]]; Flatten[ Table[ a[n, k], {n, 0, 10}, {k, 0, n}]] (* Jean-François Alcover, Aug 02 2012, from 2nd formula *)

Formula

Z(0,x) = 1, Z(1,x) = x and Z(n,x) = x*Z(n-1,x) - 2*Z(n-2,x), n >= 2.
a(n,k) = A077957(k) * A053119(n,k). - Paul Curtz, Sep 30 2011

Extensions

Edited and information added by Johannes W. Meijer, Jun 27 2011

A228439 Numbers k dividing u(k), where the Lucas sequence is defined u(i) = u(i-1) - 2*u(i-2) with initial conditions u(0)=0, u(1)=1.

Original entry on oeis.org

1, 7, 49, 343, 2401, 4753, 16807, 33271, 76783, 117649, 232897, 461041, 537481, 823543, 1630279, 3227287, 3762367, 5764801, 7447951, 11411953, 11527201, 19358969, 22591009, 26336569, 40353607, 44720977, 52135657, 79883671, 80690407
Offset: 1

Views

Author

Thomas M. Bridge, Nov 02 2013

Keywords

Comments

Since the absolute value of the discriminant of the characteristic polynomial is prime (=7), the sequence contains every nonnegative integer power of 7. Other terms are formed on multiplication of 7^k by sporadic primes.

Examples

			For k = 0, 1 , ..., 10, there is u(k) = 0,1,1,-1,-3,-1,5,7,-3,-17,-11. Clearly only k = 1 and k = 7 satisfy k divides u(k).
		

Crossrefs

Cf. A107920 (Lucas Sequence u(n)=u(n-1)-2u(n-2)).

Programs

  • Mathematica
    nn = 10000; s = LinearRecurrence[{1, -2}, {1, 1}, nn]; t = {}; Do[If[Mod[s[[n]], n] == 0, AppendTo[t, n]], {n, nn}]; t (* T. D. Noe, Nov 08 2013 *)

Extensions

a(19)-a(29) from Amiram Eldar, May 28 2024
Previous Showing 21-30 of 30 results.