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A289363
Primes p such that p^2 + p - 1 is composite.
1
7, 17, 23, 29, 37, 43, 47, 61, 67, 71, 73, 79, 97, 107, 109, 113, 127, 137, 139, 151, 157, 167, 173, 179, 197, 211, 223, 227, 229, 239, 251, 257, 269, 271, 277, 283, 293, 307, 311, 313, 317, 337, 347, 353, 359, 367, 379, 383, 389, 397, 409, 421, 439, 443, 457, 467, 479, 487, 491, 503, 509, 521, 523
OFFSET
1,1
COMMENTS
Includes all primes == 2 (mod 5) or == 3 or 7 (mod 11) except 2 and 3.
If p is in this sequence, p^2 + p is not in A241884 although p^2 + p - 1 is composite.
LINKS
MAPLE
select(t -> isprime(t) and not isprime(t^2+t-1), [seq(i, i=1..1000, 2)]);
MATHEMATICA
Select[Prime[Range[100]], CompositeQ[#^2+#-1]&] (* Jean-François Alcover, Jul 18 2017 *)
PROG
(PARI) lista(nn) = forprime(p=2, nn, if (!isprime(p^2+p-1), print1(p, ", "))); \\ Michel Marcus, Jul 05 2017
(Magma) [p: p in PrimesUpTo(600) | not IsPrime(p^2+p-1)]; // Vincenzo Librandi, Jul 05 2017
CROSSREFS
Cf. A241884.
Sequence in context: A191087 A032454 A107643 * A319040 A216838 A198441
KEYWORD
nonn
AUTHOR
Robert Israel, Jul 04 2017
STATUS
approved