A123751 - OEIS

A123751

Primes in A007406.

5, 266681, 40799043101, 86364397717734821, 36190908596780862323291147613117849902036356128879432564211412588793094572280300268379995976006474252029, 334279880945246012373031736295774418479420559664800307123320901500922509788908032831003901108510816091067151027837158805812525361841612048446489305085140033

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OFFSET

1,1

COMMENTS

A007406 lists the Wolstenholme numbers.

Numbers k such that A007406(k) is prime are listed in A111354.

LINKS

Table of n, a(n) for n=1..6.

Carlos M. da Fonseca, M. Lawrence Glasser, Victor Kowalenko, Generalized cosecant numbers and trigonometric inverse power sums, Applicable Analysis and Discrete Mathematics, Vol. 12, No. 1 (2018), 70-109.

Eric Weisstein's World of Mathematics, Harmonic Number.

Eric Weisstein's World of Mathematics, Wolstenholme's Theorem.

Eric Weisstein's World of Mathematics, Wolstenholme Number

FORMULA

a(n) = A007406(A111354(n)).

EXAMPLE

A007406 begins {1, 5, 49, 205, 5269, 5369, 266681, 1077749, 9778141, ...}.

Thus a(1) = 5 because A007406(2) = 5 is prime but A007406(1) = 1 is not prime.

a(2) = 266681 because A007406(7) = 266681 is prime but all A007406(k) are composite for 2 < k < 7.

MATHEMATICA

Do[f=Numerator[Sum[1/i^2, {i, 1, n}]]; If[PrimeQ[f], Print[{n, f}]], {n, 1, 250}]

CROSSREFS