A100331 - OEIS

%I #21 Sep 08 2022 08:45:15

%S 1,3,9,15,18,20,28,33,55,65,68,84,88,98,109,115,119,120,124,129,134,

%T 135,140,159,165,173,185,188,190,205,223,239,264,270,275,278,288,295,

%U 305,308,323,329,350,368,370,388,409,460,464,499,510,525,540,565,579,593

%N Positive integers n such that n^6 + n^5 + n^4 + n^3 + n^2 + n - 1 is prime.

%H Robert Israel, <a href="/A100331/b100331.txt">Table of n, a(n) for n = 1..10000</a>

%e 3 is in the sequence because 3^6 + 3^5 + 3^4 + 3^3 + 3^2 + 3 - 1 = 1091, which is prime.

%p A100331:=n->`if`(isprime(-1+add(n^i, i=1..6)), n, NULL): seq(A100331(n), n=1..1000); # _Wesley Ivan Hurt_, Dec 13 2015

%t Select[Range[600], PrimeQ[Sum[ #^i, {i, 6}] - 1] &] (* _Ray Chandler_, Nov 17 2004 *)

%o (Magma) [n: n in [0..700] | IsPrime(n^6+n^5+n^4+n^3+n^2+n-1)]; // _Vincenzo Librandi_, Dec 13 2015

%o (PARI) is(n) = ispseudoprime(n^6+n^5+n^4+n^3+n^2+n-1) \\ _Altug Alkan_, Dec 13 2015

%Y Cf. A100330.

%K nonn,easy

%O 1,2

%A _Ray G. Opao_, Nov 16 2004