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 A090987 a(n) is the smallest prime whose square divides the numerator of the Bernoulli number B(A090997(n)). 6
 5, 7, 5, 7, 103, 11, 5, 37, 13, 5, 7, 5, 11, 7, 5, 17, 5, 13, 7, 19, 11, 5, 7, 5, 59, 5, 11, 7, 13, 5, 23, 7, 5, 17, 37, 5, 7, 5, 13, 7, 271, 19, 5, 11, 5, 7, 37, 5, 7, 29, 13, 11, 17, 5, 5, 7, 31, 11, 5, 7, 5, 23, 5, 7, 19, 11, 5, 7, 17, 5, 13, 5, 103, 37, 7, 5, 59, 5, 11, 13, 37, 7, 5, 7, 5, 131, 19, 17, 11, 37, 5, 7, 13, 5, 7, 11, 5, 23, 5, 67, 7, 5, 41, 29, 13, 11, 7, 5, 17, 5, 19, 7, 5, 43, 13, 7, 5, 31, 37, 5, 11, 67, 7, 5, 7, 17, 5, 11, 5, 7, 23, 5, 37, 7, 19, 59, 5, 11, 13, 47, 5, 7, 5, 11, 7, 5, 13, 5, 7, 5, 7, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It appears that, except for irregular primes belonging to A094095, such as a(5) = 103, a(8) = 37 and a(26) = 59, all regular prime a(n) = p divide the corresponding numerators of the Bernoulli numbers B(A090997(n)) with indices of the form 2*k*p^2, where k > 0 is an integer. - Alexander Adamchuk, Aug 19 2006 LINKS Table of n, a(n) for n=1..152. The Bernoulli Number Page, Table of factors of the numerators of Bernoulli numbers Bn in the range n = 2..10000, 2018. S. S. Wagstaff, Jr, Prime factors of the absolute values of Bernoulli numerators, 2018. CROSSREFS Cf. A000367, A090997, A094095, A122270, A122271, A122272, A122273. Sequence in context: A010718 A247872 A306400 * A278813 A217167 A348052 Adjacent sequences: A090984 A090985 A090986 * A090988 A090989 A090990 KEYWORD nonn AUTHOR N. J. A. Sloane, Feb 28 2004 EXTENSIONS In view of the phrase "it appears", it is not clear to me that the correctness of this sequence has been rigorously established. - N. J. A. Sloane, Aug 26 2006 More terms from Alexander Adamchuk, Aug 19 2006 Various sections edited by Petros Hadjicostas, May 12 2020 Corrected and terms a(33) onward added by Max Alekseyev, Mar 16 2023 STATUS approved

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Last modified August 4 01:11 EDT 2024. Contains 374905 sequences. (Running on oeis4.)