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 A090697 Numbers n such that n^2/2 - 1 is a prime. 5
 4, 6, 8, 12, 14, 16, 20, 22, 26, 30, 34, 36, 42, 44, 48, 50, 56, 68, 72, 76, 78, 82, 84, 86, 90, 92, 98, 100, 104, 112, 118, 124, 126, 128, 138, 146, 152, 160, 162, 170, 174, 182, 184, 190, 196, 204, 216, 218, 224, 226, 230, 236, 250, 252, 254, 264, 268, 274, 280 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A066436 gives resulting primes p such that 2p+2 is square. - Ray Chandler, Dec 25 2003 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 Harvey P. Dale, Table of n, a(n) for n = 1..1000 FORMULA a(n) = 2*A066049(n) = A110558(n)/2. - Ray Chandler, Dec 25 2003 MATHEMATICA Select[Range[2, 300, 2], PrimeQ[#^2/2-1]&] (* Harvey P. Dale, Apr 05 2014 *) PROG (PARI) isok(n) = !(n % 2) && isprime(n^2/2 - 1); \\ Michel Marcus, Jul 23 2016 CROSSREFS Cf. A066049, A066436, A091176, A110558. Sequence in context: A117247 A249722 A047407 * A225508 A235036 A107303 Adjacent sequences:  A090694 A090695 A090696 * A090698 A090699 A090700 KEYWORD easy,nonn AUTHOR Giovanni Teofilatto, Dec 20 2003 EXTENSIONS Corrected and extended by Ray Chandler, Dec 25 2003 STATUS approved

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