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 A064830 a(n) = gcd(n, prime(n)^2 - 1). 4
 1, 2, 3, 4, 5, 6, 1, 8, 3, 10, 1, 12, 1, 14, 3, 8, 1, 6, 1, 20, 3, 2, 1, 24, 1, 2, 3, 4, 1, 6, 1, 8, 3, 2, 5, 12, 1, 2, 3, 8, 1, 42, 1, 4, 9, 2, 1, 48, 1, 10, 3, 4, 1, 18, 1, 8, 3, 2, 1, 60, 1, 2, 63, 16, 13, 6, 1, 4, 3, 70, 1, 72, 1, 2, 15, 4, 1, 6, 1, 80, 3, 2, 1, 84, 5, 2, 3, 8, 1, 6, 13, 4, 3, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Harry J. Smith, Table of n, a(n) for n = 1..1000 EXAMPLE A000040(20) = 71, gcd(20, (71-1)*(71+1)) = 10 * gcd(2, 7*72) = 20 = a(20). MATHEMATICA Table[ GCD[n, Prime[n]^2 - 1], {n, 1, 100} ] PROG (PARI) { for (n=1, 1000, write("b064830.txt", n, " ", gcd(n, prime(n)^2 - 1)) ) } \\ Harry J. Smith, Sep 27 2009 CROSSREFS Cf. A000040. Sequence in context: A138776 A339738 A280701 * A160377 A269165 A319655 Adjacent sequences:  A064827 A064828 A064829 * A064831 A064832 A064833 KEYWORD nonn AUTHOR Reinhard Zumkeller, Oct 23 2001 STATUS approved

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Last modified June 17 00:17 EDT 2021. Contains 345080 sequences. (Running on oeis4.)