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 1-6 of 6 results.

A251656 4-step Fibonacci sequence starting with 1,0,1,0.

Original entry on oeis.org

1, 0, 1, 0, 2, 3, 6, 11, 22, 42, 81, 156, 301, 580, 1118, 2155, 4154, 8007, 15434, 29750, 57345, 110536, 213065, 410696, 791642, 1525939, 2941342, 5669619, 10928542, 21065442, 40604945, 78268548, 150867477, 290806412, 560547382, 1080489819
Offset: 0

Views

Author

Arie Bos, Dec 06 2014

Keywords

Crossrefs

Other 4-step Fibonacci sequences are A000078, A000288, A001630, A001631, A001648, A073817, A100532, A251654, A251655, A251703, A251704, A251705.
Cf. A000336.

Programs

  • J
    NB. see A251655 for the program and apply it to 1,0,1,0.
  • Mathematica
    LinearRecurrence[Table[1, {4}], {1, 0, 1, 0}, 36] (* Michael De Vlieger, Dec 09 2014 *)

Formula

a(n+4) = a(n)+a(n+1)+a(n+2)+a(n+3).
G.f.: (-1+x+2*x^3)/(-1+x+x^2+x^3+x^4) . - R. J. Mathar, Mar 28 2025
a(n) = A000078(n+3)-A000078(n+2)-2*A000078(n). - R. J. Mathar, Mar 28 2025

A251654 4-step Fibonacci sequence starting with 0, 1, 1, 0.

Original entry on oeis.org

0, 1, 1, 0, 2, 4, 7, 13, 26, 50, 96, 185, 357, 688, 1326, 2556, 4927, 9497, 18306, 35286, 68016, 131105, 252713, 487120, 938954, 1809892, 3488679, 6724645, 12962170, 24985386, 48160880, 92833081, 178941517, 344920864, 664856342, 1281551804
Offset: 0

Views

Author

Arie Bos, Dec 06 2014

Keywords

Crossrefs

Other 4-step Fibonacci sequences are A000078, A000288, A001630, A001631, A001648, A073817, A100532, A251655, A251656, A251672, A251703, A251704, A251705.

Programs

  • J
    NB. see A251655 for the program and apply it to 0,1,1,0.
  • Mathematica
    LinearRecurrence[Table[1, {4}], {0, 1, 1, 0}, 36] (* Michael De Vlieger, Dec 09 2014 *)

Formula

a(n+4) = a(n) + a(n+1) + a(n+2) + a(n+3).
G.f.: x*(-1+2*x^2)/(-1+x+x^2+x^3+x^4). - R. J. Mathar, Mar 28 2025
a(n) = A000078(n+2)-2*A000078(n). - R. J. Mathar, Mar 28 2025

A251655 4-step Fibonacci sequence starting with 0, 1, 1, 1.

Original entry on oeis.org

0, 1, 1, 1, 3, 6, 11, 21, 41, 79, 152, 293, 565, 1089, 2099, 4046, 7799, 15033, 28977, 55855, 107664, 207529, 400025, 771073, 1486291, 2864918, 5522307, 10644589, 20518105, 39549919, 76234920, 146947533, 283250477, 545982849, 1052415779, 2028596638
Offset: 0

Views

Author

Arie Bos, Dec 06 2014

Keywords

Crossrefs

Other 4-step Fibonacci sequences are A000078, A000288, A001630, A001631, A001648, A073817, A100532, A251654, A251656, A251672, A251703, A251704, A251705.

Programs

  • J
    (see www.jsoftware.com) First construct the generating matrix
       [M=: (#.@}: + {:)\"1&.|: <:/~i.4
    1 1 1 1
    1 2 2 2
    2 3 4 4
    4 6 7 8
    Given that matrix, one can produce the first 4*250 numbers with
    , M(+/ . *)^:(i.250) 0 1 1 1x
  • Mathematica
    LinearRecurrence[Table[1, {4}], {0, 1, 1, 1}, 36] (* Michael De Vlieger, Dec 09 2014 *)

Formula

a(n+4) = a(n) + a(n+1) + a(n+2) + a(n+3).
G.f.: x*(x-1)*(1+x)/(-1+x+x^2+x^3+x^4) . - R. J. Mathar, Mar 28 2025
a(n) = A000078(n+2)-A000078(n). - R. J. Mathar, Mar 28 2025

A251704 4-step Fibonacci sequence starting with 1, 1, 0, 1.

Original entry on oeis.org

1, 1, 0, 1, 3, 5, 9, 18, 35, 67, 129, 249, 480, 925, 1783, 3437, 6625, 12770, 24615, 47447, 91457, 176289, 339808, 655001, 1262555, 2433653, 4691017, 9042226, 17429451, 33596347, 64759041, 124827065, 240611904, 463794357, 893992367, 1723225693
Offset: 0

Views

Author

Arie Bos, Dec 07 2014

Keywords

Crossrefs

Other 4-step Fibonacci sequences are A000078, A000288, A001630, A001631, A001648, A073817, A100532, A251654, A251655, A251656, A251703, A251705.

Programs

  • J
    NB. see A251655 for the program and apply it to 1,1,0,1.
  • Mathematica
    LinearRecurrence[Table[1, {4}], {1, 1, 0, 1}, 36] (* Michael De Vlieger, Dec 09 2014 *)

Formula

a(n+4) = a(n) + a(n+1) + a(n+2) + a(n+3).
G.f.: (1+x)*(x^2+x-1)/(-1+x+x^2+x^3+x^4) . - R. J. Mathar, Mar 28 2025
a(n) = A001630(n-2)+A001630(n-1), n>2. - R. J. Mathar, Mar 28 2025

A251705 4-step Fibonacci sequence starting with 1, 1, 1, 0.

Original entry on oeis.org

1, 1, 1, 0, 3, 5, 9, 17, 34, 65, 125, 241, 465, 896, 1727, 3329, 6417, 12369, 23842, 45957, 88585, 170753, 329137, 634432, 1222907, 2357229, 4543705, 8758273, 16882114, 32541321, 62725413, 120907121, 233055969, 449229824, 865918327, 1669111241
Offset: 0

Views

Author

Arie Bos, Dec 07 2014

Keywords

Crossrefs

Other 4-step Fibonacci sequences are A000078, A000288, A001630, A001631, A001648, A073817, A100532, A251654, A251655, A251656, A251703, A251704.

Programs

  • J
    NB. see A251655 for the program and apply it to 1,1,1,0.
  • Mathematica
    LinearRecurrence[Table[1, {4}], {1, 1, 1, 0}, 36] (* Michael De Vlieger, Dec 09 2014 *)

Formula

a(n+4) = a(n) + a(n+1) + a(n+2) + a(n+3).
G.f.: (-1+3*x^3+x^2)/(-1+x+x^2+x^3+x^4) . - R. J. Mathar, Mar 28 2025

A320122 Numbers that are not Keith numbers in any base.

Original entry on oeis.org

12, 30, 390, 1170, 1200, 1560, 2340, 2760, 3120, 3900, 4680, 6120, 6240, 7680, 7800, 8460, 10020, 10140, 10950, 11580, 15090, 15480, 17160, 17580, 18360, 19140, 20280, 20700, 20940, 21480, 23040, 23280, 24060, 24210, 24960, 26550, 28740, 29250, 29520, 29670, 30060, 31080, 32400
Offset: 1

Views

Author

Robert FERREOL, Oct 06 2018

Keywords

Comments

A number N >= 2 is a Keith number in a base b <= N if the Fibonacci sequence u(i) whose initial terms are the t digits of N in the base b, and later terms are given by rule that u(i) = sum of t previous terms, contains N itself. Here a(n) is the n-th number N that is not a Keith number in any base b <= N.

Examples

			a(1) = 12 because 12 is not a Keith number in any base from 2 to 12, while all previous numbers are in some base.
For example, with b = 2, the sequence is : 1, 1, 0, 0, 2, 3, 5, 10, 20, ...; it doesn't contain 12. See A251703.
		

Crossrefs

Cf. A007629 (Keith numbers in base 10).

Programs

  • Maple
    fibo:=proc(n, b) local L,m,M,k:
    L:=convert(n,base,b):m:=nops(L):M:=seq(L[m+1-k],k=1..m):
    while M[m]
    				
  • PARI
    iskb(n, b) = if(nA007629
    isok(n) = if (n<=2, 0, for(b=2, n-1, if (iskb(n, b), return(0))); return (1)); \\ Michel Marcus, Oct 08 2018
  • Python
    def digits(n, b):
        r = []
        m = n
        while m > 0:
            r = [m % b] + r
            m = m // b
        return r
    def fibo(n, b):
        L = digits(n, b)
        m = len(L) - 1
        while L[m] < n:
            L.append(sum(k for k in L))
            L.pop(0)
        return L[m] == n
    def test(n):
        for b in range(2, n + 1):
            if fibo(n, b):
                return True
        return False
    print([n for n in range(2, 2001) if not test(n)])
    

Extensions

More terms from Michel Marcus, Oct 08 2018
Showing 1-6 of 6 results.