A076597 - OEIS

%I #21 May 13 2019 09:37:19

%S 4,5,6,7,8,10,11,12,13,15,17,18,21,22,23,26,28,30,32,33,37,40,41,43,

%T 46,47,48,50,52,55,56,57,58,61,62,66,67,68,70,72,78,85,87,88,91,95,96,

%U 98,102,103,105,116,117,122,127,128,132,133,136,140,142,143,146,147,150

%N Numbers k such that sqrt(k*(k-1)*(k-2)*(k-3)+1) is a prime.

%C Almost half of the values for k < 100 are primes.

%C Numbers k such that k^2 - 3k + 1 is a prime. - _Jon E. Schoenfield_, Dec 22 2017

%H Iain Fox, <a href="/A076597/b076597.txt">Table of n, a(n) for n = 1..10000</a>

%e 40 is in the sequence because sqrt(40*39*38*37 + 1) is 1481 which is prime.

%t Select[Range[150], PrimeQ[Sqrt[ #*(# - 1)*(# - 2)*(# - 3) + 1]] &] (* _Ray Chandler_, Aug 24 2006 *)

%t Select[Range[150],PrimeQ[#^2-3#+1]&] (* _Harvey P. Dale_, May 13 2019 *)

%o (PARI) isok(k) = isprime(k^2 - 3k + 1); \\ _Michel Marcus_, Dec 22 2017

%K easy,nonn

%O 1,1

%A _Ben Paul Thurston_, Oct 20 2002

%E Extended by _Ray Chandler_, Aug 24 2006