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 A089623 Numbers n such that n^2 + 2n - 1 is prime. 2
 1, 2, 4, 6, 8, 12, 14, 18, 20, 26, 28, 32, 34, 36, 42, 46, 48, 54, 60, 62, 68, 70, 74, 76, 88, 92, 102, 106, 116, 118, 120, 126, 130, 134, 138, 144, 154, 160, 168, 172, 176, 182, 190, 204, 210, 216, 222, 230, 232, 236, 238, 246, 252, 256, 258, 264, 266, 272 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Equivalently, numbers n such that (n+1)^2 - 2 is prime. REFERENCES M. Cerasoli, F. Eugeni and M. Protasi, Elementi di Matematica Discreta, Bologna 1988. Emanuele Munarini and Norma Zagaglia Salvi, Matematica Discreta, UTET, CittaStudiEdizioni, Milano 1997. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = 2*A088572(n). MATHEMATICA Select[Range[1000], PrimeQ[#^2 + 2 # - 1] &] (* Vincenzo Librandi, May 24 2014 *) PROG (MAGMA) [n: n in [0..400] | IsPrime(n^2+2*n-1)]; // Vincenzo Librandi, Dec 17 2010 (PARI) is(n)=isprime(n^2+2*n-1) \\ Charles R Greathouse IV, Jun 05 2017 CROSSREFS Cf. A088572. See A028871 for the actual primes. Sequence in context: A010063 A260652 A324102 * A089681 A227308 A214294 Adjacent sequences:  A089620 A089621 A089622 * A089624 A089625 A089626 KEYWORD nonn,easy AUTHOR Giovanni Teofilatto, Dec 31 2003 EXTENSIONS Corrected (1 prepended and 96 replaced with 92) by Vincenzo Librandi, Dec 17 2010 STATUS approved

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Last modified December 7 08:14 EST 2019. Contains 329839 sequences. (Running on oeis4.)