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 A076597 Numbers k such that sqrt(k*(k-1)*(k-2)*(k-3)+1) is a prime. 1
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified December 9 08:17 EST 2021. Contains 349627 sequences. (Running on oeis4.)