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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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Last modified September 24 16:27 EDT 2016. Contains 276522 sequences.