A058263 a(n) = gcd(prime(n) - 1, prime(n+1) - 1).

1, 2, 2, 2, 2, 4, 2, 2, 2, 2, 6, 4, 2, 2, 2, 2, 2, 6, 2, 2, 6, 2, 2, 8, 4, 2, 2, 2, 4, 14, 2, 2, 2, 2, 2, 6, 6, 2, 2, 2, 2, 10, 2, 4, 2, 6, 6, 2, 2, 4, 2, 2, 10, 2, 2, 2, 2, 6, 4, 2, 2, 2, 2, 2, 4, 2, 6, 2, 2, 4, 2, 2, 6, 6, 2, 2, 4, 4, 8, 2, 2, 10, 2, 6, 2, 2, 8, 4, 2, 2, 2, 2, 2, 2, 2, 2, 4, 2, 18, 6, 2, 2

Offset: 1

Author

Labos Elemer, Dec 06 2000

Keywords

• nonn

Examples

			a(24) = gcd(89-1, 97-1) = gcd(88, 96) = 8.
		

Links

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

Crossrefs

Cf. A006093.

Programs

Mathematica

Table[GCD[# - 1, NextPrime@ # - 1] &@ Prime@ n, {n, 102}] (* Michael De Vlieger, Dec 31 2016 *)
GCD[#[[1]],#[[2]]]&/@Partition[Prime[Range[110]]-1,2,1] (* Harvey P. Dale, Aug 26 2020 *)

PARI

a(n) = gcd(prime(n)-1, prime(n+1)-1); \\ Michel Marcus, Dec 11 2013

Formula

a(n) = gcd(A006093(n), A006093(n+1)).

Extensions

Offset corrected to 1 by Michel Marcus, Dec 11 2013