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 A326577 a(n) = (2*n - 1) / A326478(2*n - 1). 5
 1, 3, 5, 7, 3, 11, 13, 3, 17, 19, 3, 23, 5, 3, 29, 31, 3, 1, 37, 3, 41, 43, 15, 47, 7, 3, 53, 1, 3, 59, 61, 3, 5, 67, 3, 71, 73, 3, 1, 79, 3, 83, 5, 3, 89, 7, 3, 1, 97, 3, 101, 103, 15, 107, 109, 3, 113, 1, 3, 1, 11, 3, 5, 127, 3, 131, 7, 3, 137, 139, 3, 1, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA If 2*n - 1 is prime then a(n) is prime. a(n) = gcd((2*n-1)*N(2*n-2), D(2*n-2)), with N(k)/D(k) = B(k) the k-th Bernoulli number. MAPLE A326577 := n -> (2*n - 1)/A326478(2*n - 1): seq(A326577(n), n=1..72); db := n -> denom(bernoulli(n)): nb := n -> numer(bernoulli(n)): a := n -> igcd(db(2*n-2), (2*n-1)*nb(2*n-2)): seq(a(n), n=1..72); PROG (PARI) f(n) = n*denominator(n*bernfrac(n-1))/denominator(bernfrac(n-1)); \\ A326478 a(n) = (2*n-1)/f(2*n-1); \\ Michel Marcus, Jul 17 2019 CROSSREFS Cf. A326478, A326578, A027641/A027642 (Bernoulli). Sequence in context: A255562 A130140 A051417 * A090368 A120374 A088836 Adjacent sequences:  A326574 A326575 A326576 * A326578 A326579 A326580 KEYWORD nonn AUTHOR Peter Luschny, Jul 16 2019 STATUS approved

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Last modified May 17 12:55 EDT 2021. Contains 343971 sequences. (Running on oeis4.)