A138676 a(n) = prime(n)^7 mod prime(n-1).

1, 2, 3, 4, 7, 4, 9, 6, 3, 12, 6, 30, 5, 1, 4, 43, 10, 7, 36, 57, 54, 31, 60, 45, 88, 27, 7, 21, 34, 98, 1, 120, 128, 62, 128, 133, 5, 84, 44, 22, 128, 112, 128, 172, 128, 67, 210, 105, 128

Offset: 2

Author

Artur Jasinski, Mar 26 2008

Keywords

• nonn
• look

Comments

a(n) = 128 if prime(n-1) and prime(n) are twin primes and prime(n-1)>128. - Robert Israel, Feb 12 2020

Examples

			a(1)=1 because 3^7 = 1 mod 2
a(2)=2 because 5^7 = 2 mod 3
		

Links

• Robert Israel, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A001223, A038702, A138672, A138673, A138674, A138675, A138677, A138678, A138679, A138680, A138681.

Programs

Magma

[NthPrime(n)^7 mod NthPrime(n-1): n in [2..50]]; // Bruno Berselli, May 23 2011

Maple

seq(ithprime(n)&^7 mod ithprime(n-1),n=2..100); # Robert Israel, Feb 12 2020

Mathematica

Table[Mod[Prime[n]^7, Prime[n - 1]], {n, 2, 50}]
(* The following program is more efficient because it only generates each prime once, but it is less easy to understand: *)
PowerMod[Last[#],7,First[#]]&/@Partition[Prime[Range[60]],2,1] (* Harvey P. Dale, Sep 02 2016 *)

PARI

a(n) = my(p=prime(n)); lift(Mod(p, precprime(p-1))); \\ Michel Marcus, Mar 17 2023