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A089623 Numbers n such that n^2 + 2n - 1 is prime. 3
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 September 18 07:39 EDT 2020. Contains 337166 sequences. (Running on oeis4.)