A076597 Numbers k such that sqrt(k*(k-1)*(k-2)*(k-3)+1) is a prime.

4, 5, 6, 7, 8, 10, 11, 12, 13, 15, 17, 18, 21, 22, 23, 26, 28, 30, 32, 33, 37, 40, 41, 43, 46, 47, 48, 50, 52, 55, 56, 57, 58, 61, 62, 66, 67, 68, 70, 72, 78, 85, 87, 88, 91, 95, 96, 98, 102, 103, 105, 116, 117, 122, 127, 128, 132, 133, 136, 140, 142, 143, 146, 147, 150

Offset

1,1

Comments

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

Numbers k such that k^2 - 3k + 1 is a prime. - Jon E. Schoenfield, Dec 22 2017

Links

Iain Fox, Table of n, a(n) for n = 1..10000

Example

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

Mathematica

Select[Range[150], PrimeQ[Sqrt[ #*(# - 1)*(# - 2)*(# - 3) + 1]] &] (* Ray Chandler, Aug 24 2006 *)
Select[Range[150], PrimeQ[#^2-3#+1]&] (* Harvey P. Dale, May 13 2019 *)

Prog

(PARI) isok(k) = isprime(k^2 - 3k + 1); \\ Michel Marcus, Dec 22 2017

Crossrefs

Sequence in context: A065342 A231369 A251392 * A301592 A194414 A182204

Adjacent sequences: A076594 A076595 A076596 * A076598 A076599 A076600

Keyword

easy,nonn

Author

Ben Paul Thurston, Oct 20 2002

Extensions

Extended by Ray Chandler, Aug 24 2006

Status

approved