A097009 a(n) = gcd(prime(2*n)-1, prime(n)-1).

1, 2, 4, 6, 2, 12, 2, 2, 2, 14, 6, 4, 20, 2, 2, 26, 2, 30, 6, 2, 36, 6, 2, 2, 12, 2, 2, 2, 54, 56, 2, 10, 4, 6, 4, 2, 12, 2, 2, 4, 2, 36, 2, 24, 14, 2, 70, 2, 2, 12, 4, 2, 48, 2, 8, 2, 2, 10, 2, 14, 6, 2, 2, 2, 12, 2, 6, 48, 2, 4, 4, 2, 2, 4, 2, 2, 2, 2, 16, 4, 2, 10, 2, 12, 2, 34, 8, 8, 20, 6, 2, 2

Offset

1,2

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Example

a(3) = gcd(Prime(6)-1, prime(3)-1) = gcd(13-1, 5-1) = gcd(12, 4) = 4.

Mathematica

Table[GCD[Prime[2 n] - 1, Prime@ n - 1], {n, 92}] (* Michael De Vlieger, Dec 03 2015 *)

Prog

(Magma) [Gcd(NthPrime(2*n)-1, NthPrime(n)-1): n in [1..80]]; // Vincenzo Librandi, Dec 04 2015
(PARI) a(n) = gcd(prime(2*n)-1, prime(n)-1); \\ Michel Marcus, Dec 04 2015

Crossrefs

Cf. A066978 (gcd(prime(2*n)+1, prime(n)+1)).

Sequence in context: A060684 A329726 A056134 * A214213 A085593 A220336

Adjacent sequences: A097006 A097007 A097008 * A097010 A097011 A097012

Keyword

nonn

Author

Labos Elemer, Jul 26 2004

Status

approved