A108879 Numbers n such that (n-1)*n^n+1 is prime.

2, 4, 20, 93, 100, 1536, 2835

Offset

1,1

Links

Table of n, a(n) for n=1..7.

Example

2 is in the sequence because (2-1)*2^2+1 = 1*2^2+1 = 4+1 = 5, which is prime.

Mathematica

Select[Range[1000], PrimeQ[(# - 1) #^# + 1] &] (* Vincenzo Librandi, Oct 23 2014 *)

Prog

(PARI) isok(n) = isprime((n-1)*n^n+1); \\ Michel Marcus, Oct 23 2014
(Magma) [n: n in [1..1000] |IsPrime((n-1)*n^n+1)]; // Vincenzo Librandi, Oct 23 2014
(Python)
from sympy import isprime
def afind(limit, startk=0):
    for k in range(startk, limit+1):
        if isprime((k-1)*k**k + 1):
            print(k, end=", ")
afind(200) # Michael S. Branicky, Jan 01 2022

Crossrefs

Cf. A108318.

Sequence in context: A325791 A188326 A158094 * A341855 A337038 A058006

Adjacent sequences: A108876 A108877 A108878 * A108880 A108881 A108882

Keyword

hard,more,nonn

Author

Ray G. Opao, Jul 14 2005

Extensions

a(7) from Michael S. Branicky, Jan 01 2022

Status

approved