A066978 - OEIS

A066978

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

1, 4, 2, 4, 6, 2, 2, 2, 2, 6, 16, 2, 6, 4, 6, 6, 20, 2, 4, 6, 2, 2, 4, 2, 2, 6, 4, 12, 2, 6, 2, 12, 6, 2, 50, 8, 2, 4, 2, 2, 2, 14, 12, 2, 2, 40, 4, 56, 6, 2, 18, 30, 2, 18, 86, 2, 10, 2, 2, 6, 2, 6, 2, 24, 2, 6, 2, 2, 4, 10, 6, 36, 8, 22, 4, 6, 6, 2, 6, 2, 6, 2, 24, 2, 2, 2, 2, 2, 6, 2, 156, 6, 2, 4

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

Starting with a(2)=4, all terms are even. - Zak Seidov, Jul 16 2016

LINKS

Harry J. Smith and Michael De Vlieger, Table of n, a(n) for n = 1..10000 (first 1000 terms from Harry J. Smith)

EXAMPLE

a(4) = gcd(prime(8) + 1, prime(4) + 1) = gcd(19 + 1, 7 + 1) = gcd(20, 8) = 4.

MATHEMATICA

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

PROG

(PARI) { for (n=1, 1000, write("b066978.txt", n, " ", gcd(prime(2*n) + 1, prime(n) + 1)) ) } \\ Harry J. Smith, Apr 13 2010

(Magma) [Gcd(NthPrime(2*n)+1, NthPrime(n)+1): n in [1..80]]; // Vincenzo Librandi, Dec 04 2015

CROSSREFS

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

Sequence in context: A167507 A007005 A237869 * A236187 A114566 A013679

Adjacent sequences: A066975 A066976 A066977 * A066979 A066980 A066981

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Jan 26 2002

STATUS

approved