A385405 - OEIS

A385405

Decimal expansion of 1/(2*cosh(1)^2).

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

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OFFSET

0,1

LINKS

Table of n, a(n) for n=0..104.

Hideyuki Ohtsuka, Problem 11978, Problems and Solutions, The American Mathematical Monthly, Vol. 124, No. 5 (2017), p. 465; A Sum of Hyperbolic Cosines of Fibonacci Numbers, Solution to Problem 11978 by Kyle Gatesman, ibid., Vol. 126, No. 2 (2019), p. 185.

FORMULA

Equals 1/(2*A073743^2).

Equals Sum_{n>=0} (-1)^n/(cosh(Fibonacci(n)) * cosh(Fibonacci(n+3))) (Ohtsuka, 2017).

EXAMPLE

0.20998717080701303469724836952085072245859336411538...

MATHEMATICA

RealDigits[1/(2*Cosh[1]^2), 10, 120][[1]]

PROG

(PARI) 1/(2*cosh(1)^2)

CROSSREFS

Cf. A000045, A073743.

Sequence in context: A154937 A037996 A299626 * A002741 A213322 A374288

Adjacent sequences: A385402 A385403 A385404 * A385406 A385407 A385408

KEYWORD

nonn,cons,easy

AUTHOR

Amiram Eldar, Jul 25 2025

STATUS

approved