A332892 - OEIS

A332892

Decimal expansion of Sum_{k>=0} 1/(6*k)!.

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

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OFFSET

1,5

COMMENTS

For q integer >= 1, Sum_{m>=0} 1/(q*m)! = (1/q) * Sum_{k=1..q} exp(X_k) where X_1, X_2, ..., X_q are the q-th roots of unity.

REFERENCES

Serge Francinou, Hervé Gianella, Serge Nicolas, Exercices de Mathématiques, Oraux X-ENS, Analyse 2, problème 3.10, p. 182, Cassini, Paris, 2004

LINKS

Table of n, a(n) for n=1..87.

FORMULA

Equals (1/3) * (cosh(1) + 2*cosh(1/2)*cos((sqrt(3))/2)).

Sum_{k>=0} (-1)^k / (6*k)! = (cos(1) + 2*cos(1/2)*cosh(sqrt(3)/2))/3 = 0.9986111131987866537... - Vaclav Kotesovec, Mar 02 2020

Continued fraction: 1 + 1/(720 - 720/(665281 - 665280/(13366081 - ... - P(n-1)/((P(n) + 1) - ... )))), where P(n) = (6*n)*(6*n - 1)*(6*n - 2)*(6*n - 3)*(6*n - 4)*(6*n - 5) for n >= 1. Cf. A346441. - Peter Bala, Feb 22 2024

EXAMPLE

1.001388890976564743867770084409737409278656173555781142...

MAPLE

evalf(sum(1/(6*n)!, n=0..infinity), 150);

MATHEMATICA

RealDigits[(1/3)*(Cosh[1] + 2*Cosh[1/2]*Cos[Sqrt[3]/2]), 10, 120][[1]] (* Amiram Eldar, May 31 2023 *)

PROG

(PARI) sumpos(k=0, 1/(6*k)!) \\ Michel Marcus, Mar 02 2020

CROSSREFS

Cf. A001113 (Sum 1/k!), A073743 (Sum 1/(2k)!), A143819 (Sum 1/(3k)!), A332890 (Sum 1/(4k)!), A269296 (Sum 1/(5k)!), this sequence (Sum 1/(6k)!), A346441.

Sequence in context: A157471 A288094 A131596 * A371137 A140975 A065481

Adjacent sequences: A332889 A332890 A332891 * A332893 A332894 A332895

KEYWORD

nonn,cons

AUTHOR

Bernard Schott, Mar 02 2020

STATUS

approved