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 1-8 of 8 results.

A024199 a(n) = (2n-1)!! * Sum_{k=0..n-1}(-1)^k/(2k+1).

Original entry on oeis.org

0, 1, 2, 13, 76, 789, 7734, 110937, 1528920, 28018665, 497895210, 11110528485, 241792844580, 6361055257725, 163842638377950, 4964894559637425, 147721447995130800, 5066706567801827025, 171002070002301095250, 6548719685561840296125, 247199273204273879989500
Offset: 0

Views

Author

Clark Kimberling

Keywords

Comments

(2*n + 1)!!/a(n+1), n>=0, is the n-th approximant for William Brouncker's continued fraction for 4/Pi = 1 + 1^2/(2 + 3^2/(2 + 5^2/(2 + ... ))) See the C. Brezinski and J.-P. Delahaye references given under A142969 and A142970, respectively. The double factorials (2*n + 1)!! = A001147(n+1) enter. - Wolfdieter Lang, Oct 06 2008

Examples

			a(3) = (2*3 - 1)!! * Sum_{k=0..2} (-1)^k/(2k + 1) = 5!! * (1/(2*0 + 1) - 1/(2*1 + 1) + 1/(2*2 + 1)) = 5*3*1*(1/1 - 1/3 + 1/5) = 15 - 5 + 3 = 13. Notice that the first factor always cancels the common denominator of the sum. - _Michael B. Porter_, Jul 22 2016

References

  • A. E. Jolliffe, Continued Fractions, in Encyclopaedia Britannica, 11th ed., pp. 30-33; see p. 31.

Links

Crossrefs

Cf. A004041, A000407.
From Johannes W. Meijer, Nov 12 2009: (Start)
Cf. A007509 and A025547.
Equals first column of A167584.
Equals row sums of A167591.
Equals first right hand column of A167594.
(End)
Cf. A167576 and A135457.

Programs

  • Magma
    [0] cat [ n le 2 select (n) else 2*Self(n-1)+(2*n-3)^2*Self(n-2): n in [1..25] ]; // Vincenzo Librandi, Feb 17 2015
  • Maple
    a := proc(n) option remember; if n=0 then 0 elif n=1 then 1 else 2*a(n-1)+(2*n-3)^2* a(n-2) fi end: seq(a(n), n=0..20); # Peter Luschny, Nov 16 2016 after N. J. A. Sloane
  • Mathematica
    f[k_] := (2 k - 1) (-1)^(k + 1)
t[n_] := Table[f[k], {k, 1, n}]
a[n_] := SymmetricPolynomial[n - 1, t[n]]
Table[a[n], {n, 1, 22}]    (* A024199 signed *)
(* Clark Kimberling, Dec 30 2011 *)
RecurrenceTable[{a[n+1] == 2*a[n] + (2*n-1)^2*a[n-1],a[0] == 0, a[1] == 1},a,{n,0,20}] (* Vaclav Kotesovec, Mar 18 2014 *)
CoefficientList[Series[Pi/4/Sqrt[1-2*x] - 1/2*Log[2*x+Sqrt[4*x^2-1]]/Sqrt[2*x-1], {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Mar 18 2014 *)

Formula

a(n) = s(1)s(2)...s(n)(1/s(1) - 1/s(2) + ... + c/s(n)) where c=(-1)^(n+1) and s(k) = 2k-1 for k = 1, 2, 3, ... (was previous definition). - Clark Kimberling
D-finite with recurrence a(0) = 0, a(1) = 1, a(n+1) = 2*a(n) + (2*n-1)^2*a(n-1). - N. J. A. Sloane, Jul 19 2002
a(n) + A024200(n) = A001147(n) = (2n-1)!!. - Max Alekseyev, Sep 23 2007
a(n)/A024200(n) -> Pi/(4-Pi) as n -> oo. - Max Alekseyev, Sep 23 2007
From Wolfdieter Lang, Oct 06 2008: (Start)
E.g.f. for a(n+1), n>=0: (sqrt(1-2*x)+arcsin(2*x)*sqrt(1+2*x)/2)/((1-4*x^2)^(1/2)*(1-2*x)). From the recurrence, solving (1-4*x^2)y''(x)-2*(8*x+1)*y'(x)-9*y=0 with inputs y(0)=1, y'(0)=2.
a(n+1) = A003148(n) + A143165(n), n>=0 (from the two terms of the e.g.f.). (End)
From Johannes W. Meijer, Nov 12 2009: (Start)
a(n) = (-1)^(n-1)*(2*n-3)!! + (2*n-1)*a(n-1) with a(0) = 0.
a(n) = (2*n-1)!!*sum((-1)^(k)/(2*k+1), k=0..n-1)
(End)
E.g.f.: Pi/4/sqrt(1-2*x) - 1/2*log(2*x+sqrt(4*x^2-1))/sqrt(2*x-1). - Vaclav Kotesovec, Mar 18 2014
a(n) ~ Pi * 2^(n-3/2) * n^n / exp(n). - Vaclav Kotesovec, Mar 18 2014
a(n) = (2*H(n+1/2)-Gamma(n+1/2))*2^(n-2)*sqrt(Pi) with H(x) the Hadamard factorial (see the link section). - Cyril Damamme, Jul 19 2015
a(n) = A135457(n) - (-1)^n A001147(n-1). - Cyril Damamme, Jul 19 2015
a(n) = (Pi + (-1)^n*(Psi(n/2 + 1/4) - Psi(n/2 + 3/4)))*Gamma(n+1/2)*2^(n-2)/sqrt(Pi). - Robert Israel, Jul 20 2015
a(n) = A167576(n) - A135457(n). - Cyril Damamme, Jul 22 2015
a(n)/A001147(n) -> Pi/4 as n -> oo. - Daniel Suteu, Jul 21 2016
From Peter Bala, Nov 15 2016: (Start)
Conjecture: a(n) = 1/2*Sum_{k = 0..2*n-1} (-1)^(n-k+1)*k!*(2*n - 2*k - 3)!!, where the double factorial of an odd integer (positive or negative) may be defined in terms of the gamma function as (2*N - 1)!! = 2^((N+1)/2)*Gamma(N/2 + 1)/sqrt(Pi).
E.g.f. 1/2*arcsin(2*x)/sqrt(1 - 2*x) = x + 2*x^2/2! + 13*x^3/3! + 76*x^4/4! + .... (End)

Extensions

Edited by N. J. A. Sloane, Jul 19 2002
New name from Cyril Damamme, Jul 19 2015

A167572 The ED3 array read by antidiagonals.

Original entry on oeis.org

1, 5, 1, 23, 11, 1, 167, 83, 17, 1, 1473, 741, 183, 23, 1, 16413, 8169, 2043, 323, 29, 1, 211479, 106107, 26529, 4409, 503, 35, 1, 3192975, 1592235, 398025, 66345, 8175, 723, 41, 1, 54010305, 27062325, 6765975, 1127655, 140865, 13677, 983, 47, 1
Offset: 1

Views

Author

Johannes W. Meijer, Nov 10 2009

Keywords

Comments

The coefficients in the upper right triangle of the ED3 array (m>n) were found with the a(n,m) formula while the coefficients in the lower left triangle of the ED3 array (m<=n) were found with the recurrence relation, see below. We use for the array rows the letter n (>=1) and for the array columns the letter m (>=1).
For the ED1, ED2 and ED4 arrays see A167546, A167560 and A167584.

Examples

			The ED3 array begins with:
1, 1, 1, 1, 1, 1, 1, 1, 1, 1
5, 11, 17, 23, 29, 35, 41, 47, 53, 59
23, 83, 183, 323, 503, 723, 983, 1283, 1623, 2003
167, 741, 2043, 4409, 8175, 13677, 21251, 31233, 43959, 59765
1473, 8169, 26529, 66345, 140865, 266793, 464289, 756969, 1171905, 1739625
16413, 106107, 398025, 1127655, 2678325, 5623443, 10768737, 19194495, 32297805, 51834795

Links

  • Johannes W. Meijer, The four Escher-Droste arrays, jpg image, Mar 08 2013.

Crossrefs

A000012, A016969, A167573, A167574 and A167575 equal the first five rows of the array.
A167576, A167577 and A167578 equal the first three columns of the array.
A167579 equals the row sums of the ED3 array read by antidiagonals.
A167580 is a triangle related to the a(n) formulas of the rows of the ED3 array.
A167583 is a triangle related to the GF(z) formulas of the rows of the ED3 array.
Cf. A014481 (the 2^(n-1)*(n-1)!*(2*n-1) factor).
Cf. A167546 (ED1 array), A167560 (ED2 array), A167584 (ED4 array).

Formula

a(n,m) = ((2*m-1)!!/ (2*m-2*n-1)!!)*int(sinh(y*(2*n-1))/(cosh(y))^(2*m),y=0..infinity) for m>n.
The (n-1)-differences of the n-th array row lead to the recurrence relation
sum((-1)^k*binomial(n-1,k)*a(n,m-k),k=0..n-1) = 2^(n-1)*(n-1)!*(2*n-1).

A007509 Numerator of Sum_{k=0..n} (-1)^k/(2*k+1).

Original entry on oeis.org

1, 2, 13, 76, 263, 2578, 36979, 33976, 622637, 11064338, 11757173, 255865444, 1346255081, 3852854518, 116752370597, 3473755390832, 3610501179557, 3481569435902, 133330680156299, 129049485078524, 5457995496252709, 227848175409504262, 234389556075339277
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Comments

Denominators of convergents to 4/Pi. [For Brouncker's continued fraction, with numerators A025547(n+1), for n >= 0. - Wolfdieter Lang, Aug 26 2019]
See A352395 (the denominators for the present sequence) for the formula of this alternating sum, and the Abramowitz-Stegun link. - Wolfdieter Lang, Apr 06 2022

Examples

			1/1, 2/3, 13/15, 76/105, 263/315, 2578/3465, 36979/45045, 33976/45045, 622637/765765, ...

References

  • P. Beckmann, A History of Pi. Golem Press, Boulder, CO, 2nd ed., 1971, p. 131.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Crossrefs

Denominators are given in A352395.
From Johannes W. Meijer, Nov 12 2009: (Start)
Cf. A157142 and A166107.
Appears in A167576, A167577, A167578, A024199, A167588 and A167589. (End)
Cf. A142969 for the numerators of Brouncker's continued fraction of 4/Pi - 1.

Programs

  • Magma
    [Numerator(&+[(-1)^k/(2*k+1):k in [0..n]]): n in [0..23]]; // Marius A. Burtea, Aug 26 2019
  • Maple
    A007509 := n->numer(add((-1)^k/(2*k+1),k=0..n));
  • Mathematica
    Table[Numerator[FunctionExpand[(Pi + (-1)^n(HarmonicNumber[n/2 + 1/4] - HarmonicNumber[n/2 - 1/4]))/4]], {n, 0, 20}] (* Vladimir Reshetnikov, Jan 18 2011 *)
Numerator[Table[Sum[(-1)^k/(2k+1),{k,0,n}],{n,0,30}]] (* Harvey P. Dale, Oct 22 2011 *)
Table[(-1)^k/(2k+1),{k,0,30}]//Accumulate//Numerator (* Harvey P. Dale, May 03 2019 *)

Formula

a(n) = numerator((Psi(n + 3/2) - Psi((2*n - (-1)^n)/4 + 1) - log(2) + Pi/2)/2), with the digamma function Psi(z). See the formula in A352395. - Wolfdieter Lang, Apr 06 2022
a(n) = numerator(Pi/4 + (-1)^n * (Psi((n + 5/2)/2) - Psi((n + 3/2)/2))/4). - Vaclav Kotesovec, May 16 2022

Extensions

Crossref. corrected (A025547 replaced with A352395) by Wolfdieter Lang, Apr 06 2022

A167580 A triangle related to the a(n) formulas of the rows of the ED3 array A167572.

Original entry on oeis.org

1, 6, -1, 20, 0, 3, 56, 28, 98, -15, 144, 192, 1080, -48, 105, 352, 880, 7568, 2024, 6534, -945, 832, 3328, 40976, 31616, 132444, -8112, 10395, 1920, 11200, 187488, 274480, 1593960, 286900, 972162, -135135, 4352, 34816, 761600, 1784320, 13962848
Offset: 1

Views

Author

Johannes W. Meijer, Nov 10 2009

Keywords

Comments

The a(n) formulas given below correspond to the first ten rows of the ED3 array A167572.
The recurrence relations of the a(n) formulas for the left hand triangle columns, see the cross-references below, lead to the sequences A013609, A003148, A081277 and A079628.

Examples

			Row 1: a(n) = 1.
Row 2: a(n) = 6*n - 1.
Row 3: a(n) = 20*n^2 + 0*n + 3.
Row 4: a(n) = 56*n^3 + 28*n^2 + 98*n - 15.
Row 5: a(n) = 144*n^4 + 192*n^3 + 1080*n^2 - 48*n + 105.
Row 6: a(n) = 352*n^5 + 880*n^4 + 7568*n^3 + 2024*n^2 + 6534*n - 945.
Row 7: a(n) = 832*n^6 + 3328*n^5 + 40976*n^4 + 31616*n^3 + 132444*n^2 - 8112*n + 10395.
Row 8: a(n) = 1920*n^7 + 11200*n^6 + 187488*n^5 + 274480*n^4 + 1593960*n^3 + 286900*n^2 + 972162*n - 135135.
Row 9: a(n) = 4352*n^8 + 34816*n^7 + 761600*n^6 + 1784320*n^5 + 13962848*n^4 + 7874944*n^3 + 29641200*n^2 - 2080800*n + 2027025.
Row 10: a(n) = 9728*n^9 + 102144*n^8 + 2830848*n^7 + 9645312*n^6 + 98382912*n^5 + 106720416*n^4 + 522283552*n^3 + 69265488*n^2 + 255468870*n - 34459425.

Crossrefs

A167572 is the ED3 array.
A000012, A016969, A167573, A167574 and A167575 equal the first five rows of the ED3 array.
A014480, A167581, A167582, A168305 and A168306 equal the first five left hand triangle columns.
A001147 equals the first right hand triangle column.
A167576 equals the row sums.
Cf. A013609, A003148, A079628 and A081277.

Extensions

Comment and links added by Johannes W. Meijer, Nov 23 2009

A167577 The second column of the ED3 array A167572.

Original entry on oeis.org

1, 11, 83, 741, 8169, 106107, 1592235, 27062325, 514246545, 10798366635, 248374594755, 6209158112325, 167651197407225, 4861802228946075, 150717766502187675, 4973638859450709525, 174078640829054894625
Offset: 1

Views

Author

Johannes W. Meijer, Nov 10 2009

Keywords

Links

Crossrefs

Equals the second column of the ED3 array A167572.
Other columns are A167576 and A167578.
Cf. A007509 and A025547 (the sum((-1)^(k+n)/(2*k+1), k=0..n-1) factor).

Programs

  • Mathematica
    Table[(1/2)*(-1)^n*(2*n - 5)!!*((4*n^2 - 6*n - 2) + (16*n^3 - 24*n^2 - 4*n + 6)*Sum[(-1)^(k + n)/(2*k + 1), {k, 0, n - 1}]), {n, 1,50}] (* G. C. Greubel, Jun 16 2016 *)

Formula

a(n) = (1/2)*(-1)^n*(2*n-5)!!*((4*n^2-6*n-2)+(16*n^3-24*n^2-4*n+6)*sum((-1)^(k+n)/ (2*k+1), k=0..n-1)).

A167578 The third column of the ED3 array A167572.

Original entry on oeis.org

1, 17, 183, 2043, 26529, 398025, 6765975, 128556675, 2699661825, 62092533825, 1552309291575, 41912411683275, 1215458905032225, 37679245697871225, 1243414695550433175, 43519523831289457875, 1610222144582102522625
Offset: 1

Views

Author

Johannes W. Meijer, Nov 10 2009

Keywords

Links

Crossrefs

Equals the third column of the ED3 array A167572.
Other columns are A167576 and A167577.
Cf. A007509 and A025547 (the sum((-1)^(k+n)/(2*k+1), k=0..n-1) factor).

Programs

  • Mathematica
    Table[(1/4)*(-1)^(n)*(2*n - 7)!!*((8*n^4 - 20*n^3 - 22*n^2 + 55*n + 12) + (32*n^5 - 80*n^4 - 80*n^3 + 200*n^2 + 18*n - 45)*(Sum[(-1)^(k + n)/(2*k + 1), {k, 0, n - 1}])), {n, 1, 50}] (* G. C. Greubel, Jun 16 2016 *)

Formula

a(n) = (1/4)*(-1)^(n)*(2*n-7)!!*((8*n^4-20*n^3-22*n^2+55*n+12)+(32*n^5-80*n^4-80*n^3+200*n^2+18*n-45)*(sum((-1)^(k+n)/(2*k+1),k=0..n-1))).

A135457 a(n) = (2n-1)!! * Sum_{k=0..n-2}(-1)^k/(2k+1).

Original entry on oeis.org

0, 3, 10, 91, 684, 8679, 100542, 1664055, 25991640, 532354635, 10455799410, 255542155155, 6044821114500, 171748491958575, 4751436512960550, 153911731348760175, 4874807783839316400, 177334729873063945875
Offset: 1

Views

Author

Benoit Cloitre, Dec 15 2007

Keywords

Links

Crossrefs

Cf. A167576 and A024199.

Programs

  • Magma
    I:=[0,3,10]; [n le 3 select I[n] else 4*Self(n-1)+(4*n^2-12*n+1)*Self(n-2)-(8*n^2-48*n+70)*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Jul 17 2015
  • Maple
    a := n -> (2^(n-2)*GAMMA(n+1/2)*((-1)^n*(Psi(n/2+1/4)-Psi(n/2-1/4))+Pi))/sqrt(Pi);
seq(a(n), n=1..18); # Peter Luschny, Jul 18 2015
  • Mathematica
    FullSimplify[Table[(2^(n-2)*(n-1/2)!*(Pi+2*(-1)^n*LerchPhi[-1,1,n-1/2]))/Sqrt[Pi],{n,1,20}]] (* Vaclav Kotesovec, Oct 11 2013 *)
  • PARI
    a(n)=round((-1/4)*prod(i=1,n,2*i-3)*(Pi*(2*n-1)+2*(-1)^n*sum(k=0,1500,1.*k!/prod(i=1,k,(2*i+2*n-1)))))

Formula

a(n) = (-1/4)(Product_{i=1..n}(2i-3))((2n-1)Pi + 2(-1)^n*Sum_{k>=0}k!/ Product_{j=1..k}(2j+2n-1)). - Benoit Cloitre, Dec 15 2007
a(n+3) = 4*a(n+2) + (4n^2+12n+1)*a(n+1) - (8n^2-2)*a(n) with a(1)=0, a(2)=3, a(3)=10. - Benoit Cloitre, Dec 15 2007
a(n) ~ Pi * 2^(n-3/2) * n^n / exp(n). - Vaclav Kotesovec, Oct 11 2013
a(n+1) = (2n+1)*(a(n) - (-1)^n (2n-3)!!) with a(1)=0. - Cyril Damamme, Jul 16 2015
a(n) = (2^(n-2)*Gamma(n+1/2)*((-1)^n*(Psi(n/2+1/4)-Psi(n/2-1/4))+Pi))/sqrt(Pi). - Peter Luschny, Jul 18 2015
a(n) = A167576(n) - A024199(n). - Cyril Damamme, Jul 22 2015

Extensions

Definition replaced by a simplified one by Cyril Damamme, Jul 18 2015

A167583 A triangle related to the GF(z) formulas of the rows of the ED3 array A167572.

Original entry on oeis.org

1, 1, 5, 3, 14, 23, 15, 81, 73, 167, 105, 660, 414, 804, 1473, 945, 6825, 2850, 7578, 7629, 16413, 10395, 85050, 19425, 99420, 61389, 111882, 211479, 135135, 1237005, 59535, 1642725, 429525, 1461375, 1518525, 3192975, 2027025, 20540520, -2619540
Offset: 1

Views

Author

Johannes W. Meijer, Nov 10 2009

Keywords

Comments

The GF(z) formulas given below correspond to the first ten rows of the ED3 array A167572. The polynomials in their numerators lead to the triangle given above.

Examples

			Row 1: GF(z) = 1/(1-z).
Row 2: GF(z) = (z + 5)/(1-z)^2.
Row 3: GF(z) = (3*z^2 + 14*z + 23)/(1-z)^3.
Row 4: GF(z) = (15*z^3 + 81*z^2 + 73*z + 167)/(1-z)^4.
Row 5: GF(z) = (105*z^4 + 660*z^3 + 414*z^2 + 804*z + 1473)/(1-z)^5.
Row 6: GF(z) = (945*z^5 + 6825*z^4 + 2850*z^3 + 7578*z^2 + 7629*z + 16413)/(1-z)^6.
Row 7: GF(z) = (10395*z^6 + 85050*z^5 + 19425*z^4 + 99420*z^3 + 61389*z^2 + 111882*z + 211479)/(1-z)^7.
Row 8: GF(z) = (135135*z^7 + 1237005*z^6 + 59535*z^5 + 1642725*z^4 + 429525*z^3 + 1461375*z^2 + 1518525*z + 3192975)/(1-z)^8.
Row 9: GF(z) = (2027025*z^8 + 20540520*z^7 - 2619540*z^6 + 32228280*z^5 - 2479050*z^4 + 27797400*z^3 + 15813900*z^2 + 28153800*z + 54010305)/(1-z)^9.
Row 10: GF(z) = (34459425*z^9 + 383107725*z^8 - 115135020*z^7 + 722119860*z^6 - 283607730*z^5 + 703347750*z^4 + 89576100*z^3 + 470110500*z^2 + 495868185*z + 1030249845)/(1-z)^10.

Crossrefs

A167572 is the ED3 array.
A001147 equals the first left hand column.
A167576 equals the first right hand column.
A014481 equals the row sums.
Showing 1-8 of 8 results.

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