A064830 a(n) = gcd(n, prime(n)^2 - 1).

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

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: A339738 A364500 A280701 * A355582 A160377 A373028

Adjacent sequences: A064827 A064828 A064829 * A064831 A064832 A064833

Keyword

nonn

Author

Reinhard Zumkeller, Oct 23 2001

Status

approved