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Published online by Cambridge University Press: 20 November 2018
It is well known that
1
where An denotes the number of "up-down" or alternating permutations
2
of 1, 2, …, n. The numbers A2n and A2n+1 are known as the secant and tangent numbers respectively and A2n = (—l)"E2n, where En is the Euler number.