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 A123751 Primes in A007406. 2
 5, 266681, 40799043101, 86364397717734821, 36190908596780862323291147613117849902036356128879432564211412588793094572280300268379995976006474252029, 334279880945246012373031736295774418479420559664800307123320901500922509788908032831003901108510816091067151027837158805812525361841612048446489305085140033 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A007406 lists the Wolstenholme numbers. Numbers k such that A007406(k) is prime are listed in A111354. LINKS 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 Cf. A111354, A007406, A001008, A007407, A067567, A056903. Sequence in context: A038027 A237641 A057679 * A152516 A295532 A240132 Adjacent sequences:  A123748 A123749 A123750 * A123752 A123753 A123754 KEYWORD nonn AUTHOR Alexander Adamchuk, Oct 11 2006 STATUS approved

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Last modified August 13 22:39 EDT 2022. Contains 356109 sequences. (Running on oeis4.)