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.

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A002389 Decimal expansion of -log(gamma), where gamma is Euler's constant A001620.

Original entry on oeis.org

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

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Author

Keywords

Comments

From Peter Bala, Aug 24 2025: (Start)
By definition, the Euler-Mascheroni constant gamma = lim_{n -> oo} s(n), where s(n) = Sum_{k = 1..n} 1/k - log(n). The convergence is slow. For example, s(50) = 0.5(87...) is only correct to 1 decimal digit. Let S(n) = Sum_{k = 0..n} (-1)^(n+k)*binomial(n, k)*binomial(n+k, k)*s(n+k). Elsner shows that S(n) converges to gamma much more rapidly. For example, S(50) = 0.57721566490153286060651209008(02...) gives gamma correct to 29 decimal digits.
Define E(n) = Sum_{k = 0..n} (-1)^(n+k)*binomial(n, k)*binomial(n+k, k)*log(s(n+k)). Then it appears that E(n) converges rapidly to log(gamma). For example, E(50) = -0.549539312981644822337661768802(88...) gives log(gamma) correct to 30 decimal digits. Cf. A073004. (End)

Examples

			.549539312981644822337661768802907788330698981263...
		

References

  • W. E. Mansell, Tables of Natural and Common Logarithms. Royal Society Mathematical Tables, Vol. 8, Cambridge Univ. Press, 1964, p. XVIII.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Programs

  • Magma
    SetDefaultRealField(RealField(100)); R:= RealField(); -Log(EulerGamma(R)); // G. C. Greubel, Sep 07 2018
  • Mathematica
    RealDigits[-Log[EulerGamma], 10, 100][[1]] (* G. C. Greubel, Sep 07 2018 *)
  • PARI
    -log(Euler) \\ Michel Marcus, Mar 11 2013
    

A094644 Continued fraction for e^gamma.

Original entry on oeis.org

1, 1, 3, 1, 1, 3, 5, 4, 1, 1, 2, 2, 1, 7, 9, 1, 16, 1, 1, 1, 2, 6, 1, 2, 1, 6, 2, 59, 1, 1, 1, 3, 3, 3, 2, 1, 3, 5, 100, 1, 58, 1, 2, 1, 94, 1, 1, 2, 2, 10, 1, 2, 7, 1, 3, 4, 5, 3, 10, 1, 21, 1, 11, 1, 4, 1, 2, 2, 1, 2, 2, 1, 8, 3, 2, 1, 1, 6, 1, 2, 2, 1, 38, 2, 1, 4, 1, 3, 1, 1, 5, 3, 1, 52, 1, 2, 2, 1, 1
Offset: 0

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Author

Keywords

Comments

Increasing partial quotients are: 1,3,5,7,9,16,59,100,129,314,2294,1568705
e^gamma appears in theorems of Mertens, Gronwall, Ramanujan, and Robin on primes, the sum-of-divisors function, and the Riemann Hypothesis (see Caveney-Nicolas-Sondow 2011, pp. 1-2).

Examples

			1 + 1/(1 + 1/(3 + 1/(1 + 1/(1 + 1/(3 + 1/(5 + 1/(4 + ...)))))))
		

References

  • J. Havil, Gamma, Exploring Euler's Constant, Princeton University Press, Princeton and Oxford, 2003, page 97.
  • G. Boros and V. Moll, Irresistible Integrals: Symbolics, Analysis and Experiments in the Evaluation of Integrals, Cambridge University Press, Cambridge, 2004, Chap. 10.

Crossrefs

Cf. A073004 = decimal expansion of exp(gamma).
Gamma is the Euler-Mascheroni constant A001620.
Cf. A079650 = continued fraction for exp(-gamma). [From R. J. Mathar, Sep 05 2008]

Programs

  • Mathematica
    ContinuedFraction[ Exp[ EulerGamma], 100]
  • PARI
    contfrac(exp(Euler)) \\ Amiram Eldar, Jun 13 2021

Extensions

Offset changed by Andrew Howroyd, Aug 07 2024

A236435 Numerator of Product_{k=1..n-1} (1 + 1/prime(k)).

Original entry on oeis.org

1, 3, 2, 12, 96, 1152, 2304, 41472, 165888, 3981312, 119439360, 3822059520, 7644119040, 321052999680, 1284211998720, 61642175938560, 3328677500682240, 199720650040934400, 399441300081868800, 1597765200327475200, 115039094423578214400, 230078188847156428800, 18406255107772514304000
Offset: 1

Views

Author

Jonathan Sondow, Feb 01 2014

Keywords

Comments

A236436(n)/(a(n)*zeta(2)) is the asymptotic density of the prime(n-1)-rough squarefree numbers (squarefree numbers whose prime factors are all >= prime(n-1)) for n >= 2. E.g., A236436(2)/(a(2)*zeta(2)) = 2/(3*zeta(2)) = 4/Pi^2 (A185199) is the asymptotic density of the odd squarefree numbers (A056911), and A236436(3)/(a(3)*zeta(2)) = 1/(2*zeta(2)) = 3/Pi^2 (A104141) is the asymptotic density of the 5-rough squarefree numbers (A276378). - Amiram Eldar, Aug 26 2025

Examples

			(1 + 1/2)*(1 + 1/3)*(1 + 1/5)*(1 + 1/7) = 96/35 has numerator a(5) = 96.
Fractions begin with 1, 3/2, 2, 12/5, 96/35, 1152/385, 2304/715, 41472/12155, 165888/46189, 3981312/1062347, 119439360/30808063, 3822059520/955049953, ...
		

References

  • G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 5th ed., Oxford Univ. Press, 1979; Theorem 429.

Crossrefs

Programs

  • Mathematica
    Numerator@Table[ Product[ 1 + 1/Prime[ k], {k, 1, n-1}], {n, 1, 23}]

Formula

a(n+1) / A236436(n+1) = (A072045(n)/A072044(n)) / (A038110(n+1)/A060753(n+1)) because 1+x = (1-x^2) / (1-x).
a(n) / A236436(n) = Product_{k=1..n-1} (1 + 1/prime(k)) ~ (6/Pi^2)*exp(gamma)*log(n) as n -> infinity, by Mertens's theorem.

A052488 a(n) = floor(n*H(n)) where H(n) is the n-th harmonic number, Sum_{k=1..n} 1/k (A001008/A002805).

Original entry on oeis.org

1, 3, 5, 8, 11, 14, 18, 21, 25, 29, 33, 37, 41, 45, 49, 54, 58, 62, 67, 71, 76, 81, 85, 90, 95, 100, 105, 109, 114, 119, 124, 129, 134, 140, 145, 150, 155, 160, 165, 171, 176, 181, 187, 192, 197, 203, 208, 214, 219, 224, 230, 235, 241, 247, 252, 258, 263, 269
Offset: 1

Views

Author

Tomas Mario Kalmar (TomKalmar(AT)aol.com), Mar 15 2000

Keywords

Comments

Floor(n*H(n)) gives a (very) rough approximation to the n-th prime.
a(n) is the integer part of the solution to the Coupon Collector's Problem. For example, if there are n=4 different prizes to collect from cereal boxes and they are equally likely to be found, then the integer part of the average number of boxes to buy before the collection is complete is a(4)=8. - Ron Lalonde (ronronronlalonde(AT)hotmail.com), Feb 04 2004

References

  • John D. Barrow, One Hundred Essential Things You Didn't Know You Didn't Know, Ch. 3, 'On the Cards', W. W. Norton & Co., NY & London, 2008, pp. 30-32.

Crossrefs

Programs

  • Magma
    [Floor(n*HarmonicNumber(n)): n in [1..60]]; // G. C. Greubel, May 14 2019
    
  • Maple
    for n from 1 to 100 do printf(`%d,`,floor(n*sum(1/k, k=1..n))) od:
    # Alternatively:
    A052488:= n -> floor(n*(Psi(n+1)+gamma));
    seq(A052488(n),n=1..100); # Robert Israel, May 19 2014
  • Mathematica
    f[n_] := Floor[n*HarmonicNumber[n]]; Array[f, 60] (* Robert G. Wilson v, Nov 23 2015 *)
  • PARI
    a(n) = floor(n*sum(k=1, n, 1/k)) \\ Altug Alkan, Nov 23 2015
    
  • Python
    from math import floor
    n=100 #number of terms
    ans=0
    finalans = []
    for i in range(1, n+1):
        ans+=(1/i)
        finalans.append(floor(ans*i))
    print(finalans)
    # Adam Hugill, Feb 14 2022
    
  • Python
    from fractions import Fraction
    from itertools import count, islice
    def agen():
        Hn = 0
        for n in count(1):
            Hn += Fraction(1, n)
            yield (n*Hn.numerator)//Hn.denominator
    print(list(islice(agen(), 60))) # Michael S. Branicky, Aug 10 2022
    
  • Python
    from sympy import harmonic
    def A052488(n): return int(n*harmonic(n)) # Chai Wah Wu, Oct 24 2023
  • Sage
    [floor(n*harmonic_number(n)) for n in (1..60)] # G. C. Greubel, May 14 2019
    

Extensions

More terms from James Sellers, Mar 17 2000

A091724 Decimal expansion of e^(2*EulerGamma).

Original entry on oeis.org

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

Views

Author

Eric W. Weisstein, Feb 01 2004

Keywords

Examples

			3.17221895812545052772791340906947497712295773777230...
		

Crossrefs

Programs

  • Mathematica
    RealDigits[Exp[2*EulerGamma], 10, 100][[1]] (* Amiram Eldar, Jun 25 2021 *)
  • PARI
    exp(2*Euler) \\ Michel Marcus, Jun 25 2021

Formula

Equals lim_{x -> 0} e^(2*ExpIntegralEi(-x))/x^2.
Equals A073004^2. - Michel Marcus, Jun 25 2021
Equals lim sup_{n->oo} H(n)/log_2(n)^2, where H(n) = A370689(n)/A370690(n) (De Koninck and Luca, 2007). - Amiram Eldar, Feb 27 2024

A227242 Decimal expansion of (e^gamma - 1)/e^gamma.

Original entry on oeis.org

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

Views

Author

Arkadiusz Wesolowski, Oct 19 2013

Keywords

Comments

The value is equal to lim_{n->oo} (Sum_{d|n#, d>n} 1/phi(d))/(Sum_{d|n#} 1/phi(d)).

Examples

			(exp(gamma) - 1)/exp(gamma) = 0.438540516433114830175856785....
		

Crossrefs

Programs

  • Magma
    E:=EulerGamma(RealField(105)); Reverse(Intseq(Floor(10^105*(Exp(E)-1)/Exp(E))));
    
  • Maple
    evalf(1-exp(-gamma), 120);  # Alois P. Heinz, Feb 24 2022
  • Mathematica
    RealDigits[(E^EulerGamma - 1)/E^EulerGamma, 10, 50][[1]] (* G. C. Greubel, Oct 02 2017 *)
  • PARI
    default(realprecision, 105); x=10*(exp(Euler)-1)/exp(Euler); for(n=1, 105, d=floor(x); x=(x-d)*10; print1(d, ", "));

Formula

From Alois P. Heinz, Feb 24 2022: (Start)
Equals 1 - exp(-gamma) = 1 - A080130.
Equals lim_{n->oo} A351901(n)/A000142(n). (End)

A059565 Beatty sequence for e^gamma (gamma is the Euler-Mascheroni constant A001620).

Original entry on oeis.org

1, 3, 5, 7, 8, 10, 12, 14, 16, 17, 19, 21, 23, 24, 26, 28, 30, 32, 33, 35, 37, 39, 40, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 64, 65, 67, 69, 71, 73, 74, 76, 78, 80, 81, 83, 85, 87, 89, 90, 92, 94, 96, 97, 99, 101, 103, 105, 106, 108, 110, 112, 113, 115, 117
Offset: 1

Views

Author

Mitch Harris, Jan 22 2001

Keywords

Crossrefs

Cf. A073004. Beatty complement is A059566.

Programs

  • Magma
    R:=RealField(100); [Floor(Exp(EulerGamma(R))*n): n in [1..100]]; // G. C. Greubel, Aug 27 2018
  • Mathematica
    Table[ Floor[ n * E^EulerGamma], {n, 1, 70} ]
  • PARI
    { default(realprecision, 100); b=exp(1)^Euler; for (n = 1, 2000, write("b059565.txt", n, " ", floor(n*b)); ) } \\ Harry J. Smith, Jun 28 2009
    

A379367 Numerators of the partial sums of the reciprocals of the squarefree kernel function (A007947).

Original entry on oeis.org

1, 3, 11, 7, 38, 27, 199, 117, 386, 793, 8933, 1553, 20574, 41863, 127591, 71303, 1227166, 2539417, 48759433, 24864701, 25095646, 50632187, 1174239991, 605711068, 125604071, 252924241, 267797099, 19356010, 564511331, 1891973791, 58959268151, 31867258958, 8730535499
Offset: 1

Views

Author

Amiram Eldar, Dec 21 2024

Keywords

Examples

			Fractions begin with 1, 3/2, 11/6, 7/3, 38/15, 27/10, 199/70, 117/35, 386/105, 793/210, 8933/2310, 1553/385, ...
		

References

  • Jean-Marie De Koninck and Aleksandar Ivić, Topics in Arithmetical Functions, North-Holland Publishing Company, Amsterdam, Netherlands, 1980. See pp. 16-17.

Crossrefs

Cf. A007947, A073355, A370896, A379368 (denominators), A379369.

Programs

  • Mathematica
    rad[n_] := Times @@ FactorInteger[n][[;;, 1]]; Numerator[Accumulate[Table[1/rad[n], {n, 1, 50}]]]
  • PARI
    rad(n) = vecprod(factor(n)[, 1]);
    list(nmax) = {my(s = 0); for(k = 1, nmax, s += 1 / rad(k); print1(numerator(s), ", "))};

Formula

a(n) = numerator(Sum_{k=1..n} 1/A007947(k)).
a(n)/A379368(n) = exp((1 + o(1)) * sqrt(8*log(n)/log(log(n)))).
a(n)/A379368(n) ~ (1/2) * exp(gamma) * F(log(n)) * log(log(n)), where F(t) = (6/Pi^2) * Sum_{m>=1} min(1,exp(t)/m)/Product_{primes p|m} (p+1).

A119806 Decimal expansion of cos(gamma).

Original entry on oeis.org

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

Views

Author

T. D. Noe, May 24 2006

Keywords

Comments

This is the real part of exp(i*gamma), where gamma is the Euler-Mascheroni constant A001620. See A119807 for the imaginary part. The constant exp(gamma) (A073004) appears in many formulas. Does exp(i*gamma)?

Examples

			0.8379852878801965399549928612589497248086592013241766579...
		

Crossrefs

Cf. A001620 (Euler-Mascheroni constant), A073004, A119807.

Programs

  • Magma
    SetDefaultRealField(RealField(100)); R:= RealField(); Cos(EulerGamma(R)); // G. C. Greubel, Aug 30 2018
  • Mathematica
    RealDigits[Cos[EulerGamma],10,150][[1]]
  • PARI
    default(realprecision, 100); cos(Euler) \\ G. C. Greubel, Aug 30 2018
    

Formula

Equals 2 * e * lim_{n->oo} (sin(gamma(n))-sin(gamma))*(n!)^(1/n), where gamma(n) = Sum_{k=1..n} 1/k - log(n) (Bătineţu-Giurgiu, 2021). - Amiram Eldar, Apr 02 2022

A119807 Decimal expansion of sin(gamma).

Original entry on oeis.org

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

Views

Author

T. D. Noe, May 24 2006

Keywords

Comments

This is the imaginary part of exp(i*gamma), where gamma is the Euler-Mascheroni constant A001620. See A119806 for the real part. The constant exp(gamma) (A073004) appears in many formulas. Does exp(i*gamma)?

Examples

			0.54569282320399278815735650016143074350378810920522...
		

Programs

  • Magma
    SetDefaultRealField(RealField(100)); R:= RealField(); Sin(EulerGamma(R)); // G. C. Greubel, Aug 30 2018
  • Mathematica
    RealDigits[Sin[EulerGamma],10,150][[1]]
  • PARI
    default(realprecision, 100); sin(Euler) \\ G. C. Greubel, Aug 30 2018
    
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