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.

A001203 Simple continued fraction expansion of Pi.

Original entry on oeis.org

3, 7, 15, 1, 292, 1, 1, 1, 2, 1, 3, 1, 14, 2, 1, 1, 2, 2, 2, 2, 1, 84, 2, 1, 1, 15, 3, 13, 1, 4, 2, 6, 6, 99, 1, 2, 2, 6, 3, 5, 1, 1, 6, 8, 1, 7, 1, 2, 3, 7, 1, 2, 1, 1, 12, 1, 1, 1, 3, 1, 1, 8, 1, 1, 2, 1, 6, 1, 1, 5, 2, 2, 3, 1, 2, 4, 4, 16, 1, 161, 45, 1, 22, 1, 2, 2, 1, 4, 1, 2, 24, 1, 2, 1, 3, 1, 2, 1
Offset: 0

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Author

Keywords

Comments

The first 5821569425 terms were computed by Eric W. Weisstein on Sep 18 2011.
The first 10672905501 terms were computed by Eric W. Weisstein on Jul 17 2013.
The first 15000000000 terms were computed by Eric W. Weisstein on Jul 27 2013.
The first 30113021586 terms were computed by Syed Fahad on Apr 27 2021.

Examples

			Pi = 3.1415926535897932384...
   = 3 + 1/(7 + 1/(15 + 1/(1 + 1/(292 + ...))))
   = [a_0; a_1, a_2, a_3, ...] = [3; 7, 15, 1, 292, ...].
		

References

  • P. Beckmann, "A History of Pi".
  • C. Brezinski, History of Continued Fractions and Padé Approximants, Springer-Verlag, 1991; pp. 151-152.
  • John H. Conway and Richard K. Guy, The Book of Numbers, New York: Springer-Verlag, 1996. See p. 186.
  • J. R. Goldman, The Queen of Mathematics, 1998, p. 50.
  • R. S. Lehman, A Study of Regular Continued Fractions. Report 1066, Ballistic Research Laboratories, Aberdeen Proving Ground, Maryland, Feb 1959.
  • G. Lochs, Die ersten 968 Kettenbruchnenner von Pi. Monatsh. Math. 67 1963 311-316.
  • C. D. Olds, Continued Fractions, Random House, NY, 1963; front cover of paperback edition.
  • 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).
  • James J. Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, 1999, page 274.

Crossrefs

Cf. A000796 for decimal expansion. See A007541 or A033089, A033090 for records.

Programs

  • Maple
    cfrac (Pi,70,'quotients'); # Zerinvary Lajos, Feb 10 2007
  • Mathematica
    ContinuedFraction[Pi, 98]
  • PARI
    contfrac(Pi) \\ contfracpnqn(%) is also useful!
    
  • PARI
    { allocatemem(932245000); default(realprecision, 21000); x=contfrac(Pi); for (n=1, 20000, write("b001203.txt", n, " ", x[n])); } \\ Harry J. Smith, Apr 14 2009
    
  • Python
    import itertools as it; import sympy as sp
    list(it.islice(sp.continued_fraction_iterator(sp.pi),100))
    # Nicholas Stefan Georgescu, Feb 27 2023
  • Sage
    continued_fraction(RealField(333)(pi)) # Peter Luschny, Feb 16 2015
    

Extensions

Word "Simple" added to the title by David Covert, Dec 06 2016

A002965 Interleave denominators (A000129) and numerators (A001333) of convergents to sqrt(2).

Original entry on oeis.org

0, 1, 1, 1, 2, 3, 5, 7, 12, 17, 29, 41, 70, 99, 169, 239, 408, 577, 985, 1393, 2378, 3363, 5741, 8119, 13860, 19601, 33461, 47321, 80782, 114243, 195025, 275807, 470832, 665857, 1136689, 1607521, 2744210, 3880899, 6625109, 9369319, 15994428, 22619537
Offset: 0

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Author

Keywords

Comments

Denominators of Farey fraction approximations to sqrt(2). The fractions are 1/0, 0/1, 1/1, 2/1, 3/2, 4/3, 7/5, 10/7, 17/12, .... See A082766(n+2) or A119016 for the numerators. "Add" (meaning here to add the numerators and add the denominators, not to add the fractions) 1/0 to 1/1 to make the fraction bigger: 2/1. Now 2/1 is too big, so add 1/1 to make the fraction smaller: 3/2, 4/3. Now 4/3 is too small, so add 3/2 to make the fraction bigger: 7/5, 10/7, ... Because the continued fraction for sqrt(2) is all 2's, it will always take exactly two terms here to switch from a number that's bigger than sqrt(2) to one that's less. A097545/A097546 gives the similar sequence for Pi. A119014/A119015 gives the similar sequence for e. - Joshua Zucker, May 09 2006
The principal and intermediate convergents to 2^(1/2) begin with 1/1, 3/2 4/3, 7/5, 10/7; essentially, numerators=A143607, denominators=A002965. - Clark Kimberling, Aug 27 2008
(a(2n)*a(2n+1))^2 is a triangular square. - Hugh Darwen, Feb 23 2012
a(2n) are the interleaved values of m such that 2*m^2+1 and 2*m^2-1 are squares, respectively; a(2n+1) are the interleaved values of their corresponding integer square roots. - Richard R. Forberg, Aug 19 2013
Coefficients of (sqrt(2)+1)^n are a(2n)*sqrt(2)+a(2n+1). - John Molokach, Nov 29 2015
Apart from the first two terms, this is the sequence of denominators of the convergents of the continued fraction expansion sqrt(2) = 1/(1 - 1/(2 + 1/(1 - 1/(2 + 1/(1 - ....))))). - Peter Bala, Feb 02 2017
Limit_{n->infinity} a(2n+1)/a(2n) = sqrt(2); lim_{n->infinity} a(2n)/a(2n-1) = (2+sqrt(2))/2. - Ctibor O. Zizka, Oct 28 2018

Examples

			The convergents are rational numbers given by the recurrence relation p/q -> (p + 2*q)/(p + q). Starting with 1/1, the next three convergents are (1 + 2*1)/(1 + 1) = 3/2, (3 + 2*2)/(3 + 2) = 7/5, and (7 + 2*5)/(7 + 5) = 17/12. The sequence puts the denominator first, so a(2) through a(9) are 1, 1, 2, 3, 5, 7, 12, 17. - _Michael B. Porter_, Jul 18 2016
		

References

  • C. Brezinski, History of Continued Fractions and Padé Approximants. Springer-Verlag, Berlin, 1991, p. 24.
  • Jay Kappraff, Musical Proportions at the Basis of Systems of Architectural Proportion both Ancient and Modern, in Volume I of K. Williams and M.J. Ostwald (eds.), Architecture and Mathematics from Antiquity to the Future, DOI 10.1007/978-3-319-00143-2_27, Springer International Publishing Switzerland 2015. See Eq. 32.7.
  • Serge Lang, Introduction to Diophantine Approximations, Addison-Wesley, New York, 1966.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • Guelena Strehler, Chess Fractal, April 2016, p. 24.

Crossrefs

Cf. A000129(n) = a(2n), A001333(n) = a(2n+1).

Programs

  • GAP
    a:=[0,1];; for n in [3..45] do a[n]:=a[n-1]+a[n-2-((n-1) mod 2)]; od; a; # Muniru A Asiru, Oct 28 2018
  • Haskell
    import Data.List (transpose)
    a002965 n = a002965_list !! n
    a002965_list = concat $ transpose [a000129_list, a001333_list]
    -- Reinhard Zumkeller, Jan 01 2014
    
  • JavaScript
    a=new Array(); a[0]=0; a[1]=1;
    for (i=2;i<50;i+=2) {a[i]=a[i-1]+a[i-2];a[i+1]=a[i]+a[i-2];}
    document.write(a); // Jon Perry, Sep 12 2012
    
  • Magma
    I:=[0,1,1,1]; [n le 4 select I[n] else 2*Self(n-2)+Self(n-4): n in [1..50]]; // Vincenzo Librandi, Nov 30 2015
    
  • Maple
    A002965 := proc(n) option remember; if n <= 0 then 0; elif n <= 3 then 1; else 2*A002965(n-2)+A002965(n-4); fi; end;
    A002965:=-(1+2*z+z**2+z**3)/(-1+2*z**2+z**4); # conjectured by Simon Plouffe in his 1992 dissertation; gives sequence except for two leading terms
  • Mathematica
    LinearRecurrence[{0, 2, 0, 1}, {0, 1, 1, 1}, 42] (* Vladimir Joseph Stephan Orlovsky, Feb 13 2012 *)
    With[{c=Convergents[Sqrt[2],20]},Join[{0,1},Riffle[Denominator[c], Numerator[c]]]] (* Harvey P. Dale, Oct 03 2012 *)
  • PARI
    a(n)=if(n<4,n>0,2*a(n-2)+a(n-4))
    
  • PARI
    x='x+O('x^100); concat(0, Vec((x+x^2-x^3)/(1-2*x^2-x^4))) \\ Altug Alkan, Dec 04 2015
    

Formula

a(n) = 2*a(n-2) + a(n-4) if n>3; a(0)=0, a(1)=a(2)=a(3)=1.
a(2*n) = a(2*n-1) + a(2*n-2) and a(2*n+1) = 2*a(2*n) - a(2*n-1).
G.f.: (x+x^2-x^3)/(1-2*x^2-x^4).
a(0)=0, a(1)=1, a(n) = a(n-1) + a(2*[(n-2)/2]). - Franklin T. Adams-Watters, Jan 31 2006
For n > 0, a(2*n) = a(2*n-1) + a(2*n-2) and a(2*n+1) = a(2*n) + a(2*n-2). - Jon Perry, Sep 12 2012
a(n) = (((sqrt(2) - 2)*(-1)^n + 2 + sqrt(2))*(1 + sqrt(2))^(floor(n/2)) - ((2 + sqrt(2))*(-1)^n -2 + sqrt(2))*(1 - sqrt(2))^(floor(n/2)))/8. - Ilya Gutkovskiy, Jul 18 2016
a(n) = a(n-1) + a(n-2-(n mod 2)); a(0)=0, a(1)=1. - Ctibor O. Zizka, Oct 28 2018

Extensions

Thanks to Michael Somos for several comments which improved this entry.

A119016 Numerators of "Farey fraction" approximations to sqrt(2).

Original entry on oeis.org

1, 0, 1, 2, 3, 4, 7, 10, 17, 24, 41, 58, 99, 140, 239, 338, 577, 816, 1393, 1970, 3363, 4756, 8119, 11482, 19601, 27720, 47321, 66922, 114243, 161564, 275807, 390050, 665857, 941664, 1607521, 2273378, 3880899, 5488420, 9369319, 13250218, 22619537, 31988856
Offset: 0

Views

Author

Joshua Zucker, May 08 2006

Keywords

Comments

"Add" (meaning here to add the numerators and add the denominators, not to add the fractions) 1/0 to 1/1 to make the fraction bigger: 2/1. Now 2/1 is too big, so add 1/1 to make the fraction smaller: 3/2, 4/3. Now 4/3 is too small, so add 3/2 to make the fraction bigger: 7/5, 10/7, ... Because the continued fraction for sqrt(2) is all 2s, it will always take exactly two terms here to switch from a number that's bigger than sqrt(2) to one that's less. a(n+2) = A082766(n).
a(2n) are the interleaved values of m such that 2*m^2-2 and 2*m^2+2 are squares, respectively; a(2n+1) are the corresponding integer square roots. - Richard R. Forberg, Aug 19 2013
Apart from the first two terms, this is the sequence of numerators of the convergents of the continued fraction expansion sqrt(2) = 1/(1 - 1/(2 + 1/(1 - 1/(2 + 1/(1 - ....))))). - Peter Bala, Feb 02 2017

Examples

			The fractions are 1/0, 0/1, 1/1, 2/1, 3/2, 4/3, 7/5, 10/7, 17/12, ...
		

Crossrefs

Cf. A097545, A097546 gives the similar sequence for Pi. A119014, A119015 gives the similar sequence for e. A002965 gives the denominators for this sequence. Also very closely related to A001333, A052542 and A000129.
See A082766 for another version.

Programs

  • Maple
    f:= gfun:-rectoproc({a(n+4)=2*a(n+2) +a(n),a(0)=1,a(1)=0,a(2)=1,a(3)=2}, a(n), remember):
    map(f, [$0..100]); # Robert Israel, Jun 10 2015
  • Mathematica
    f[x_, n_] := (m = Floor[x]; f0 = {m, m+1/2, m+1}; r = ({a___, b_, c_, d___} /; b < x < c) :> {b, (Numerator[b] + Numerator[c]) / (Denominator[b] + Denominator[c]), c}; Join[{m, m+1}, NestList[# /. r &, f0, n-3][[All, 2]]]); Join[{1, 0 }, f[Sqrt[2], 38]] // Numerator (* Jean-François Alcover, May 18 2011 *)
    LinearRecurrence[{0, 2, 0, 1}, {1, 0, 1, 2}, 40] (* and *) t = {1, 2}; Do[AppendTo[t, t[[-2]] + t[[-1]]]; AppendTo[t, t[[-3]] + t[[-1]]], {n, 30}]; t (* Vladimir Joseph Stephan Orlovsky, Feb 13 2012 *)
    a0 := LinearRecurrence[{2, 1}, {1, 1}, 20]; (*     A001333 *)
    a1 := LinearRecurrence[{2, 1}, {0, 2}, 20]; (* 2 * A000129 *)
    Flatten[MapIndexed[{a0[[#]],a1[[#]]} &, Range[20]]] (* Gerry Martens, Jun 09 2015 *)
  • PARI
    x='x+O('x^50); Vec((1 - x^2 + 2*x^3)/(1 - 2*x^2 - x^4)) \\ G. C. Greubel, Oct 20 2017

Formula

From Joerg Arndt, Feb 14 2012: (Start)
a(0) = 1, a(1) = 0, a(2n) = a(2n-1) + a(2n-2), a(2n+1) = a(2n) + a(2n-2).
G.f.: (1 - x^2 + 2*x^3)/(1 - 2*x^2 - x^4). (End)
a(n) = 1/4*(1-(-1)^n)*(-2+sqrt(2))*(1+sqrt(2))*((1-sqrt(2))^(1/2*(n-1))-(1+sqrt(2))^(1/2*(n-1)))+1/4*(1+(-1)^n)*((1-sqrt(2))^(n/2)+(1+sqrt(2))^(n/2)). - Gerry Martens, Nov 04 2012
a(2n) = A001333(n). a(2n+1) = A052542(n) for n>0. - R. J. Mathar, Feb 05 2024

A097545 Numerators of "Farey fraction" approximations to Pi.

Original entry on oeis.org

1, 0, 1, 2, 3, 4, 7, 10, 13, 16, 19, 22, 25, 47, 69, 91, 113, 135, 157, 179, 201, 223, 245, 267, 289, 311, 333, 355, 688, 1043, 1398, 1753, 2108, 2463, 2818, 3173, 3528, 3883, 4238, 4593, 4948, 5303, 5658, 6013, 6368, 6723, 7078, 7433, 7788, 8143, 8498, 8853
Offset: 0

Views

Author

N. J. A. Sloane, Aug 28 2004

Keywords

Comments

Given a real number x >= 1 (here x = Pi), start with 1/0 and 0/1 and construct the sequence of fractions f_n = r_n/s_n such that:
f_{n+1} = (r_k + r_n)/(s_k + s_n) where k is the greatest integer < n such that f_k <= x <= f_n. Sequence gives values r_n.
Write a 0 if f_n <= x and a 1 if f_n > x. This gives (for x = Pi) the sequence 1, 0, 0, 0, 1, 1, 1, 1, 0 (7 times), 1 (15 times), 0, 1, ... Ignore the initial string 1, 0, 0, 0, which is always the same. Look at the run lengths of the remaining sequence, which are in this case L_1 = 4, L_2 = 7, L_3 = 15, L_4 = 1, L_5 = 292, etc. (A001203). Christoffel showed that x has the continued fraction representation (L_1 - 1) + 1/(L_2 + 1/(L_3 + 1/(L_4 + ...))).

Examples

			The fractions are 1/0, 0/1, 1/1, 2/1, 3/1, 4/1, 7/2, 10/3, 13/4, 16/5, 19/6, 22/7, 25/8, 47/15, ...
		

References

  • C. Brezinski, History of Continued Fractions and Padé Approximants, Springer-Verlag, 1991; pp. 151-152.
  • E. B. Christoffel, Observatio arithmetica, Ann. Math. Pura Appl., (II) 6 (1875), 148-153.

Crossrefs

Cf. A097546.

Programs

  • Mathematica
    f[x_, n_] := (m = Floor[x]; f0 = {m, m+1/2, m+1};
    r = ({a___, b_, c_, d___} /; b < x < c) :> {b, (Numerator[b] + Numerator[c]) / (Denominator[b] + Denominator[c]), c}; Join[{m, m+1}, NestList[# /. r &, f0, n-3][[All, 2]]]); Join[{1, 0, 1, 2}, f[Pi, 48]] // Numerator  (* Jean-François Alcover, May 18 2011 *)

Extensions

More terms from Joshua Zucker, May 08 2006

A119014 Numerators of "Farey fraction" approximations to e.

Original entry on oeis.org

1, 0, 1, 2, 3, 5, 8, 11, 19, 30, 49, 68, 87, 106, 193, 299, 492, 685, 878, 1071, 1264, 1457, 2721, 4178, 6899, 9620, 12341, 15062, 17783, 20504, 23225, 25946, 49171, 75117, 124288, 173459, 222630, 271801, 320972, 370143, 419314, 468485, 517656, 566827
Offset: 0

Views

Author

Joshua Zucker, May 08 2006

Keywords

Comments

"Add" (meaning here to add the numerators and add the denominators, not to add the fractions) 1/0 to 1/1 to make the fraction bigger: 2/1, 3/1. Now 3/1 is too big, so add 2/1 to make the fraction smaller: 5/2, 8/3, 11/4. Now 11/4 is too small, so add 8/3 to make the fraction bigger: 19/7, ...

Examples

			The fractions are 1/0, 0/1, 1/1, 2/1, 3/1, 5/2, 8/3, 11/4, 19/7, ...
		

Crossrefs

For another version see A006258.
Cf. A097545, A097546 gives the similar sequence for pi. A119015 gives the denominators for this sequence.

Programs

  • Mathematica
    f[x_, n_] := (m = Floor[x]; f0 = {m, m + 1/2, m + 1}; r = ({a___, b_, c_, d___} /; b < x < c) :> {b, (Numerator[b] + Numerator[c]) / (Denominator[b] + Denominator[c]), c};
     Join[{m, m + 1}, NestList[# /. r &, f0, n - 3][[All, 2]]]); Join[{1, 0, 1 }, f[E, 41]] // Numerator
    (* Jean-François Alcover, May 18 2011 *)

A119015 Denominators of "Farey fraction" approximations to e.

Original entry on oeis.org

0, 1, 1, 1, 1, 2, 3, 4, 7, 11, 18, 25, 32, 39, 71, 110, 181, 252, 323, 394, 465, 536, 1001, 1537, 2538, 3539, 4540, 5541, 6542, 7543, 8544, 9545, 18089, 27634, 45723, 63812, 81901, 99990, 118079, 136168, 154257, 172346, 190435, 208524, 398959, 607483
Offset: 0

Views

Author

Joshua Zucker, May 08 2006

Keywords

Comments

"Add" (meaning here to add the numerators and add the denominators, not to add the fractions) 1/0 to 1/1 to make the fraction bigger: 2/1, 3/1. Now 3/1 is too big, so add 2/1 to make the fraction smaller: 5/2, 8/3, 11/4. Now 11/4 is too small, so add 8/3 to make the fraction bigger: 19/7, ...

Examples

			The fractions are 1/0, 0/1, 1/1, 2/1, 3/1, 5/2, 8/3, 11/4, 19/7, ...
		

Crossrefs

For another version see A006259.
Cf. A097545, A097546 gives the similar sequence for pi. A119014 gives the numerators for this sequence.

Programs

  • Mathematica
    f[x_, n_] := (m = Floor[x]; f0 = {m, m+1/2, m+1}; r = ({a___, b_, c_, d___} /; b < x < c) :> {b, (Numerator[b] + Numerator[c]) / (Denominator[b] + Denominator[c]), c};
     Join[{m, m+1}, NestList[# /. r &, f0, n-3][[All, 2]]]);
    Join[{0, 1, 1}, f[E, 43] // Denominator]
    (* Jean-François Alcover, May 18 2011 *)
Showing 1-6 of 6 results.