A191715 - OEIS

%I #18 Sep 08 2022 08:45:57

%S 1,133,54871,1253659,31438345,863585785,25867844011,840625753991,

%T 29488048443085,1111334648458165,44804977347486175,

%U 1924820469011714611,87800711122303545361,4238935318038328143857,11582179256389013503203871,652184749150919163867112021

%N Nonprime numbers of the form n*(n-1)^n - (n-1)*n^(n-1) + 1.

%C If n=3, then 3*2^3-2*3^2+1=7 is prime, so 7 is not in this sequence. If n=5, then 5*4^5-4*5^4+1=2621 is prime.

%H Charles R Greathouse IV, <a href="/A191715/b191715.txt">Table of n, a(n) for n = 1..377</a>

%t Union[Select[Table[n(n-1)^n-(n-1)n^(n-1)+1,{n,30}],!PrimeQ[#]&]] (* _Harvey P. Dale_, Jun 19 2011 *)

%o (Magma) [ a: n in [2..40] | not IsPrime(a) where a is n*(n-1)^n-(n-1)*n^(n-1)+1 ]; // _Vincenzo Librandi_, Jun 13 2011

%o (PARI) for(n=1,1e3,if(!ispseudoprime(k=n*(n-1)^n-(n-1)*n^(n-1)+1),print1(k", ")))

%Y Cf. A191409, A191699.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Jun 12 2011