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A326426 E.g.f.: 2*cosh(1) - Sum_{n>=0} (1 + x^n)^n * exp(-x^n) / n!. 4
1, 0, 0, -4, 6, -8, 0, -12, -8400, 40304, 0, -20, -12640320, -24, 0, -50854003228, 523588665600, -32, 0, -36, -47601422668800, -351419178958848040, 0, -44, -2657154018657032294400, 60321372390731612159952, 0, -3140712271670490316800052, -542080978696857600000, -56, 0, -60, -348600503774477204939323514880000, -50178168859710075748378214400064, 0, -1161795736961405183891091750912000068 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

More generally, the following sums are equal:

(1) 2*cosh(p*r) - Sum_{n>=0} (q^n + p)^n * exp(-p*q^n*r) * r^n/n!,

(2) 2*cosh(p*r) - Sum_{n>=0} (q^n - p)^n * exp(+p*q^n*r) * r^n/n!,

under suitable conditions; here, p = 1, q = x, r = 1.

LINKS

Paul D. Hanna, Table of n, a(n) for n = 0..520

FORMULA

E.g.f.: 2*cosh(1) - Sum_{n>=0} (1 + x^n)^n * exp(-x^n) / n!.

E.g.f.: 2*cosh(1) - Sum_{n>=0} (-1)^n * (1 - x^n)^n * exp(x^n) / n!.

a(4*n+2) = 0 for n >= 0.

EXAMPLE

E.g.f.: A(x) = 1 - 4*x^3/3! + 6*x^4/4! - 8*x^5/5! - 12*x^7/7! - 8400*x^8/8! + 40304*x^9/9! - 20*x^11/11! - 12640320*x^12/12! - 24*x^13/13! - 50854003228*x^15/15! + 523588665600*x^16/16! - 32*x^17/17! - 36*x^19/19! - 47601422668800*x^20/20! - 351419178958848040*x^21/21! - 44*x^23/23! - 2657154018657032294400*x^24/24! + 60321372390731612159952*x^25/25! + ...

such that

A(x) = 2*cosh(1) - (exp(-1) + (1+x)*exp(-x) + (1+x^2)^2*exp(-x^2)/2! + (1+x^3)^3*exp(-x^3)/3! + (1+x^4)^4*exp(-x^4)/4! + (1+x^5)^5*exp(-x^5)/5! + ...)

also

A(x) = 2*cosh(1) - (exp(1) - (1-x)*exp(x) + (1-x^2)^2*exp(x^2)/2! - (1-x^3)^3*exp(x^3)/3! + (1-x^4)^4*exp(x^4)/4! - (1-x^5)^5*exp(x^5)/5! +- ...).

RELATED SERIES.

Below we illustrate the following identity at specific values of x:

2*cosh(1) - Sum_{n>=0} (1 + x^n)^n * exp(-x^n) / n!  =  2*cosh(1) - Sum_{n>=0} (-1)^n * (1 - x^n)^n * exp(x^n) / n!.

(1) At x = 1/2, the following sums are equal

S1 = 2*cosh(1) - Sum_{n>=0} (1 + 1/2^n)^n * exp(-1/2^n) / n!,

S1 = 2*cosh(1) - Sum_{n>=0} (1 - 1/2^n)^n * exp(1/2^n) * (-1)^n / n!,

where S1 = 0.92958560659999209901292951379518757326414006011141201017999...

(2) At x = 1/e, the following sums are equal

S2 = (e + 1/e) - Sum_{n>=0} (1 + 1/e^n)^n * e^(-1/e^n) / n!,

S2 = (e + 1/e) - Sum_{n>=0} (1 - 1/e^n)^n * e^(1/e^n) * (-1)^n / n!,

where S2 = 0.97087981067504743501007428564669808856438405820315797815416...

Compare the sums for S2 to the dual identity (cf. A326428)

S3 = (e + 1/e) - Sum_{n>=0} (1 - 1/e^n)^n * e^(-1/e^n) / n!,

S3 = (e + 1/e) - Sum_{n>=0} (1 + 1/e^n)^n * e^(1/e^n) * (-1)^n / n!,

where S3 = 1.77058869998597108214121594912015480934002883992351165553600...

PROG

(PARI) /* quick informal code for the initial 120 terms */

\p500

Vec(round(serlaplace( 2*cosh(1) - sum(n=0, 500, (1 + x^n +O(x^121))^n * exp(-x^n +O(x^121)) * 1./n! ) )))

CROSSREFS

Cf. A326425, A326427, A326428.

Sequence in context: A004786 A263357 A195387 * A272028 A181097 A206798

Adjacent sequences:  A326423 A326424 A326425 * A326427 A326428 A326429

KEYWORD

sign

AUTHOR

Paul D. Hanna, Jul 03 2019

STATUS

approved

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Last modified August 15 16:02 EDT 2020. Contains 336505 sequences. (Running on oeis4.)