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 1-7 of 7 results.

A006206 Number of aperiodic binary necklaces of length n with no subsequence 00, excluding the necklace "0".

Original entry on oeis.org

1, 1, 1, 1, 2, 2, 4, 5, 8, 11, 18, 25, 40, 58, 90, 135, 210, 316, 492, 750, 1164, 1791, 2786, 4305, 6710, 10420, 16264, 25350, 39650, 61967, 97108, 152145, 238818, 374955, 589520, 927200, 1459960, 2299854, 3626200, 5720274, 9030450, 14263078
Offset: 1

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Author

Keywords

Comments

Bau-Sen Du (1985/1989)'s Table 1 has this sequence, denoted A_{n,1}, as the second column. - Jonathan Vos Post, Jun 18 2007

Examples

			Necklaces are: 1, 10, 110, 1110; 11110, 11010, 111110, 111010, ...
		

References

  • Miklos Bona, editor, Handbook of Enumerative Combinatorics, CRC Press, 2015, page 499.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A006207 (A_{n,2}), A006208 (A_{n,3}), A006209 (A_{n,4}), A130628 (A_{n,5}), A208092 (A_{n,6}), A006210 (D_{n,2}), A006211 (D_{n,3}), A094392.
Cf. A001461 (partial sums), A000045, A008683, A027750.
Cf. A125951 and A113788 for similar sequences.

Programs

  • Haskell
    a006206 n = sum (map f $ a027750_row n) `div` n where
       f d = a008683 (n `div` d) * (a000045 (d - 1) + a000045 (d + 1))
    -- Reinhard Zumkeller, Jun 01 2013
    
  • Maple
    with(numtheory): with(combinat):
    A006206 := proc(n) local sum; sum := 0; for d in divisors(n) do sum := sum + mobius(n/d)*(fibonacci(d+1)+fibonacci(d-1)) end do; sum/n; end proc:
  • Mathematica
    a[n_] := Total[(MoebiusMu[n/#]*(Fibonacci[#+1] + Fibonacci[#-1]) & ) /@ Divisors[n]]/n;
    (* or *) a[n_] := Sum[LucasL[k]*MoebiusMu[n/k], {k, Divisors[n]}]/n; Table[a[n], {n,100}] (* Jean-François Alcover, Jul 19 2011, after given formulas *)
  • PARI
    a(n)=if(n<1,0,sumdiv(n,d,moebius(n/d)*(fibonacci(d-1)+fibonacci(d+1)))/n)
    
  • Sage
    z = PowerSeriesRing(ZZ, 'z').gen().O(30)
    r = (1 - (z + z**2))
    F = -z*r.derivative()/r
    [sum(moebius(n//d)*F[d] for d in divisors(n))//n for n in range(1, 24)] # F. Chapoton, Apr 24 2020

Formula

Euler transform is Fibonacci(n+1): 1/((1 - x) * (1 - x^2) * (1 - x^3) * (1 - x^4) * (1 - x^5)^2 * (1 - x^6)^2 * ...) = 1/(Product_{n >= 1} (1 - x^n)^a(n)) = 1 + x + 2*x^2 + 3*x^3 + 5*x^4 + 8*x^5 + ...
Coefficients of power series of natural logarithm of the infinite product Product_{n>=1} (1 - x^n - x^(2*n))^(-mu(n)/n), where mu(n) is the Moebius function. This is related to Fibonacci sequence since 1/(1 - x^n - x^(2*n)) expands to a power series whose terms are Fibonacci numbers.
a(n) = (1/n) * Sum_{d|n} mu(n/d) * (Fibonacci(d-1) + Fibonacci(d+1)) = (1/n) * Sum_{d|n} mu(n/d) * Lucas(d). Hence Lucas(n) = Sum_{d|n} d*a(d).
a(n) = round((1/n) * Sum_{d|n} mu(d)*phi^(n/d)), n > 2. - David Broadhurst [Formula corrected by Jason Yuen, Dec 29 2024]
G.f.: Sum_{n >= 1} -mu(n) * log(1 - x^n - x^(2*n))/n.
a(n) = (1/n) * Sum_{d|n} mu(d) * A001610(n/d - 1), n > 1. - R. J. Mathar, Mar 07 2009
For n > 2, a(n) = A060280(n) = A031367(n)/n.

A006208 Generalized Fibonacci numbers A_{n,3}.

Original entry on oeis.org

1, 1, 0, 1, 0, 2, 1, 3, 2, 6, 4, 9, 8, 18, 16, 32, 32, 61, 64, 115, 128, 224, 258, 431, 520, 850, 1050, 1673, 2128, 3328, 4320, 6649, 8788, 13366, 17920, 26957, 36610, 54634, 74932, 111057, 153656, 226514, 315616, 463243, 649334, 949823, 1337984, 1951760
Offset: 1

Views

Author

Keywords

Comments

Bau-Sen Du's [1985/2007] Table 1, p. 6, has this sequence as the 4th column. - Jonathan Vos Post, Jun 18 2007

References

  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A006206 (A_{n,1}), A006207 (A_{n,2}), A006209 (A_{n,4}), A130628 (A_{n,5}), A208092 (A_{n,6}), A006210 (D_{n,2}), A006211 (D_{n,3}), A094392.

Programs

  • Mathematica
    max = 50;
    Do[Do[b1[1][j, n] = 0; b1[2][j, n] = 1; b2[1][j, n] = b2[2][j, n] = 0, {j, n}]; b2[1][n, n] = b2[2][n, n] = 1, {n, max}];
    Do[Do[Do[b1[k][j, n] = b1[k-2][1, n] + b1[k-2][j+1, n]; b2[k][j, n] = b2[k - 2][1, n] + b2[k-2][j+1, n], {j, n-1}]; b1[k][n, n] = b1[k-2][1, n] + b1[k-1][n, n]; b2[k][n, n] = b2[k-2][1, n] + b2[k-1][n, n], {n, max}], {k, 3, max}];
    phin[n_] := Table[b2[m][n, n] + 2 Sum[If[m+2-2j > 0, b1[m+2-2j][j, n], 0], {j, n}], {m, max}];
    MT[s_] := Table[DivisorSum[n, MoebiusMu[#] s[[n/#]]&]/n, {n, Length[s]}];
    MT[phin[3]] (* Jean-François Alcover, Oct 01 2018, after Max Alekseyev in A006207 *)
  • PARI
    \\ implementation of MT() and phin() is given in A006207
    MT(phin(3)) \\ sequence A_{n,3} \\ Max Alekseyev, Feb 23 2012

Extensions

arxiv URL replaced with non-cached version, and duplicate of a reference removed, by R. J. Mathar, Oct 30 2009
Terms a(32) onward from Max Alekseyev, Feb 23 2012

A006209 Generalized Fibonacci numbers A_{n,4}.

Original entry on oeis.org

1, 1, 0, 1, 0, 2, 0, 3, 1, 6, 2, 9, 4, 18, 8, 30, 16, 56, 32, 101, 64, 191, 128, 351, 256, 668, 512, 1257, 1026, 2402, 2056, 4592, 4122, 8854, 8272, 17092, 16608, 33212, 33364, 64674, 67072, 126490, 134912, 248038, 271528, 487986, 546818, 962350
Offset: 1

Views

Author

Keywords

References

  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A006206 (A_{n,1}), A006207 (A_{n,2}), A006208 (A_{n,3}), A130628 (A_{n,5}), A208092 (A_{n,6}), A006210 (D_{n,2}), A006211 (D_{n,3}), A094392.

Programs

  • Mathematica
    max = 100; Clear[b1, b2];
    For[n = 1, n <= max, n++,
    For[j = 1, j <= n, j++, b1[1][j, n] = 0; b1[2][j, n] = 1; b2[1][j, n] = b2[2][j, n] = 0];
    b2[1][n, n] = b2[2][n, n] = 1];
    For[k = 3, k <= max, k++,
    For[n = 1, n <= max, n++,
    For[j = 1, j <= n-1, j++, b1[k][j, n] = b1[k-2][1, n] + b1[k-2][j+1, n]; b2[k][j, n] = b2[k-2][1, n] + b2[k-2][j+1, n]];
    b1[k][n, n] = b1[k-2][1, n] + b1[k-1][n, n]; b2[k][n, n] = b2[k-2][1, n] + b2[k-1][n, n]
    ]];
    phin[n_] := Table[b2[m][n, n] + 2 Sum[If[m + 2 - 2 j > 0, b1[m + 2 - 2j][j, n], 0], {j, 1, n}], {m, 1, max}];
    MT[s_List] := Table[DivisorSum[n, MoebiusMu[#] s[[n/#]]&]/n, {n, 1, Length[s]}];
    MT[phin[4]] (* Jean-François Alcover, Nov 05 2018, adapted from Max Alekseyev's PARI script *)
  • PARI
    \\ implementation of MT() and phin() is given in A006207
    MT(phin(4)) \\ sequence A_{n,4} \\ Max Alekseyev, Feb 23 2012

Extensions

Terms a(32) onward from Max Alekseyev, Feb 23 2012

A094392 Antidiagonals of the tables formed from b(m,2,n,n), which is defined in Du 1989.

Original entry on oeis.org

1, 1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 5, 1, 1, 1, 1, 2, 8, 1, 1, 1, 1, 1, 3, 13, 1, 1, 1, 1, 1, 1, 5, 21, 1, 1, 1, 1, 1, 1, 2, 7, 34, 1, 1, 1, 1, 1, 1, 1, 3, 11, 55, 1, 1, 1, 1, 1, 1, 1, 1, 5, 16, 89, 1, 1, 1, 1, 1, 1, 1, 1, 2, 7, 25, 144, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 11, 37, 233, 1, 1, 1, 1, 1, 1, 1, 1, 1
Offset: 1

Views

Author

Amy Robinson (amylou(AT)mchsi.com), Apr 28 2004

Keywords

Examples

			E.g., for m = 5 and n = 2, b(5,2,2,2)= b(3,2,1,2) + b(4,2,2,2)= 2 because of the definition in the reference.
    1   1  1  1  1 1 1 1 1 1 1 1 1 1 1
    1   1  1  1  1 1 1 1 1 1 1 1 1 1 1
    2   1  1  1  1 1 1 1 1 1 1 1 1 1 1
    3   1  1  1  1 1 1 1 1 1 1 1 1 1 1
    5   2  1  1  1 1 1 1 1 1 1 1 1 1 1
    8   3  1  1  1 1 1 1 1 1 1 1 1 1 1
   13   5  2  1  1 1 1 1 1 1 1 1 1 1 1
   21   7  3  1  1 1 1 1 1 1 1 1 1 1 1
   34  11  5  2  1 1 1 1 1 1 1 1 1 1 1
   55  16  7  3  1 1 1 1 1 1 1 1 1 1 1
   89  25 11  5  2 1 1 1 1 1 1 1 1 1 1
  144  37 15  7  3 1 1 1 1 1 1 1 1 1 1
  233  57 23 11  5 2 1 1 1 1 1 1 1 1 1
  377  85 32 15  7 3 1 1 1 1 1 1 1 1 1
  610 130 49 23 11 5 2 1 1 1 1 1 1 1 1
		

Crossrefs

Cf. A006206 (A_{n,1}), A006207 (A_{n,2}), A006208 (A_{n,3}), A006209 (A_{n,4}), A130628 (A_{n,5}), A208092 (A_{n,6}), A006210 (D_{n,2}), A006211 (D_{n,3}), A094392.

Programs

  • Maple
    b := proc(k,i,j,n) option remember; if k = 1 then if i = 1 then return 0; end if; if i = 2 then if j = n then return 1; end if; return 0; end if; end if; if k = 2 then if i = 1 then return 1; end if; if i = 2 then if j = n then return 1; end if; return 0; end if; end if; if j = n then return b(k-2, i, 1, n) + b(k-1, i, n, n); end if; return b(k-2, i, 1, n) + b(k-2, i, j+1, n); end proc; # Chris Deugau (deugaucj(AT)uvic.ca), Dec 19 2005
  • Mathematica
    b[k_, i_, j_, n_] := b[k, i, j, n] = Which[k == 1, Which[i == 1, 0, i == 2 , If[j == n, 1, 0], True, 0], k == 2, Which[i == 1, 1, i == 2, If[j == n, 1, 0], True, 0], j == n, b[k - 2, i, 1, n] + b[k - 1, i, n, n], True, b[k - 2, i, 1, n] + b[k - 2, i, j + 1, n]];
    a[m_, n_] := b[m, 2, n, n];
    Table[a[m - n + 1, n], {m, 1, 14}, {n, m, 1, -1}] // Flatten (* Jean-François Alcover, Nov 21 2017, adapted from Maple *)

Formula

For i=2 and k >= 1 b(k+2, 2, n, n)=b(k, 2, 1, n) + b(k+1, 2, n, n). The remaining portion for the recurrence is defined in Du 1989.

Extensions

Corrected and extended by Chris Deugau (deugaucj(AT)uvic.ca), Dec 19 2005
Typo 891 -> 89,1 corrected by Jean-François Alcover, Nov 21 2017

A006207 Generalized Fibonacci numbers A_{n,2}.

Original entry on oeis.org

1, 1, 0, 1, 1, 2, 2, 3, 4, 6, 8, 11, 16, 23, 32, 46, 66, 94, 136, 195, 282, 408, 592, 856, 1248, 1814, 2646, 3858, 5644, 8246, 12088, 17706, 25992, 38155, 56102, 82490, 121474, 178902, 263776, 389033, 574304, 848069, 1253344, 1852926, 2741164
Offset: 1

Views

Author

Keywords

Comments

Bau-Sen Du (1985)'s Table 1, p. 6, has this sequence as the third column. - Jonathan Vos Post, Jun 18 2007

References

  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A006206 (A_{n,1}), A006208 (A_{n,3}), A006209 (A_{n,4}), A130628 (A_{n,5}), A208092 (A_{n,6}), A006210 (D_{n,2}), A006211 (D_{n,3}), A094392.

Programs

  • Mathematica
    max = 100; Clear[b1, b2]; For[n=1, n <= max, n++, For[j=1, j <= n, j++, b1[1][j, n] = 0; b1[2][j, n] = 1; b2[1][j, n] = b2[2][j, n] = 0]; b2[1][n, n] = b2[2][n, n] = 1]; For[k=3, k <= max, k++, For[n=1, n <= max, n++, For[j=1, j <= n-1, j++, b1[k][j, n] = b1[k-2][1, n] + b1[k - 2][j+1, n]; b2[k][j, n] = b2[k-2][1, n] + b2[k-2][j+1, n]; ]; b1[k][n, n] = b1[k-2][1, n] + b1[k-1][n, n]; b2[k][n, n] = b2[k-2][1, n] + b2[k - 1][n, n]]];
    phin[n_] := Table[b2[m][n, n] + 2*Sum[If[m + 2 - 2*j > 0, b1[m + 2 - 2*j][j, n], 0], {j, 1, n}], {m, 1, max}];
    MT[s_List] := Table[ DivisorSum[n, MoebiusMu[#]*s[[n/#]]&]/n, {n, 1, Length[s]}];
    MT[phin[2]] (* Jean-François Alcover, Dec 07 2015, adapted from Max Alekseyev's PARI script *)
  • PARI
    b1 = vector(100,k,matrix(100,100)); b2 = vector(100,k,matrix(100,100)); for(n=1,100, for(j=1,n, b1[1][j,n]=0; b1[2][j,n]=1; b2[1][j,n] = b2[2][j,n] = 0); b2[1][n,n] = b2[2][n,n] = 1); for(k=3,100, for(n=1,100, for(j=1,n-1, b1[k][j,n] = b1[k-2][1,n] + b1[k-2][j+1,n]; b2[k][j,n] = b2[k-2][1,n] + b2[k-2][j+1,n]; ); b1[k][n,n] = b1[k-2][1,n] + b1[k-1][n,n]; b2[k][n,n] = b2[k-2][1,n] + b2[k-1][n,n]; )); \\ Computing arrays b(k,1,j,n) and b(k,2,j,n)
    { phin(n) = vector(100,m, b2[m][n,n] + 2*sum(j=1,n, if(m+2-2*j>0, b1[m+2-2*j][j,n]))) } \\ sequence phi_n
    { MT(s) = vector(#s,n,sumdiv(n,d,moebius(d)*s[n/d])/n) } \\ Moebius transform
    MT( phin(2) ) \\ sequence A_{n,2}
    \\ Max Alekseyev, Feb 23 2012

Extensions

arxiv URL replaced with non-cached version by R. J. Mathar, Oct 30 2009
Terms a(32) onward from Max Alekseyev, Feb 23 2012

A130628 Related to the minimal number of periodic orbits of periods guaranteed by Sharkovskii's theorem.

Original entry on oeis.org

1, 1, 0, 1, 0, 2, 0, 3, 0, 6, 1, 9, 2, 18, 4, 30, 8, 56, 16, 99, 32, 186, 64, 337, 128, 635, 256, 1177, 512, 2220, 1024, 4176, 2048, 7930, 4098, 15044, 8200, 28738, 16410, 54937, 32848, 105474, 65760, 202845, 131668, 391316, 263680, 756223, 528128
Offset: 1

Views

Author

Jonathan Vos Post, Jun 18 2007

Keywords

Comments

Bau-Sen Du's [1985/2007] Table 1, p. 6, has this sequence as the 6th column, denoted A_{n,5}.

Crossrefs

Cf. A006206 (A_{n,1}), A006207 (A_{n,2}), A006208 (A_{n,3}), A006209 (A_{n,4}), A208092 (A_{n,6}), A006210 (D_{n,2}), A006211 (D_{n,3}), A094392.

Programs

  • Mathematica
    max = 50; Clear[b1, b2];
    For[n = 1, n <= max, n++,
    For[j = 1, j <= n, j++, b1[1][j, n] = 0; b1[2][j, n] = 1; b2[1][j, n] = b2[2][j, n] = 0]; b2[1][n, n] = b2[2][n, n] = 1];
    For[k = 3, k <= max, k++,
    For[n = 1, n <= max, n++,
    For[j = 1, j <= n-1, j++, b1[k][j, n] = b1[k-2][1, n] + b1[k-2][j+1, n]; b2[k][j, n] = b2[k-2][1, n] + b2[k-2][j+1, n]]; b1[k][n, n] = b1[k-2][1, n] + b1[k-1][n, n]; b2[k][n, n] = b2[k-2][1, n] + b2[k-1][n, n]]];
    phin[n_] := Table[b2[m][n, n] + 2 Sum[If[m + 2 - 2j > 0, b1[m + 2 - 2j][j, n], 0], {j, 1, n}], {m, 1, max}];
    MT[s_List] := Table[DivisorSum[n, MoebiusMu[#] s[[n/#]] &]/n, {n, 1, Length[s]}];
    MT[phin[5]] (* Jean-François Alcover, Nov 06 2018, adapted from Max Alekseyev's PARI script *)
  • PARI
    \\ implementation of MT() and phin() is given in A006207
    MT(phin(5)) \\ sequence A_{n,5} \\ Max Alekseyev

Extensions

Terms a(32) onward from Max Alekseyev, Feb 23 2012

A208092 Generalized Fibonacci numbers A_{n,6}.

Original entry on oeis.org

1, 1, 0, 1, 0, 2, 0, 3, 0, 6, 0, 9, 1, 18, 2, 30, 4, 56, 8, 99, 16, 186, 32, 335, 64, 630, 128, 1163, 256, 2187, 512, 4096, 1024, 7748, 2048, 14628, 4096, 27814, 8192, 52889, 16386, 101002, 32776, 193117, 65562, 370338, 131152, 711158, 262368, 1368768
Offset: 1

Views

Author

Max Alekseyev, Feb 23 2012

Keywords

Crossrefs

Cf. A006206 (A_{n,1}), A006207 (A_{n,2}), A006208 (A_{n,3}), A006209 (A_{n,4}), A130628 (A_{n,5}), A006210 (D_{n,2}), A006211 (D_{n,3}), A094392.

Programs

  • PARI
    \\ implementation of MT() and phin() is given in A006207
    MT(phin(6)) \\ sequence A_{n,6}
    /* From Max Alekseyev */
Showing 1-7 of 7 results.