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A137291
Numbers n such that prime(n)^2-2 is prime.
6
1, 2, 3, 4, 6, 8, 10, 12, 14, 15, 18, 20, 24, 27, 28, 31, 32, 34, 40, 43, 47, 48, 51, 52, 55, 62, 65, 68, 72, 82, 86, 87, 91, 94, 99, 100, 104, 107, 111, 119, 123, 128, 129, 130, 132, 133, 134, 135, 139, 141, 150, 152, 170, 172, 177, 180, 182, 191, 200, 202, 209, 211
OFFSET
1,2
COMMENTS
For n>=1, for these and only these numbers n, A242719(n) = prime(n)^2 + 1. Since A242719(n) >= prime(n)^2 + 1, then the equality is obtained on this and only this sequence.- Vladimir Shevelev, Sep 04 2014
A103960(a(n)) - A210481(a(n)) = 1. - Reinhard Zumkeller, Jul 30 2015
LINKS
FORMULA
a(n) = A049084(A049002(n)). - R. J. Mathar, Apr 09 2008
EXAMPLE
prime(24)*prime(24)-2 = 89*89-2 = 7919 is prime, so n=24 belongs to the sequence.
PROG
(Haskell)
a137291 n = a137291_list !! (n-1)
a137291_list = filter ((== 1) . a010051' . a049001) [1..]
-- Reinhard Zumkeller, Jul 30 2015
(PARI) is(n, p=prime(n))=isprime(p^2-2) \\ Charles R Greathouse IV, Feb 17 2017
KEYWORD
easy,nonn
AUTHOR
Ctibor O. Zizka, Apr 05 2008
EXTENSIONS
More terms from R. J. Mathar, Apr 09 2008
Offset corrected by Reinhard Zumkeller, Jul 30 2015
STATUS
approved