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A097009 a(n) = gcd(prime(2*n)-1, prime(n)-1). 2
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 (list; graph; refs; listen; history; text; internal format)
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: A071294 A060684 A056134 * A214213 A085593 A220336

Adjacent sequences:  A097006 A097007 A097008 * A097010 A097011 A097012

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 26 2004

STATUS

approved

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Last modified September 28 13:00 EDT 2016. Contains 276601 sequences.