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A104278 Numbers n such that 2n+1 and 2n-1 are not primes. 7
13, 17, 25, 28, 32, 38, 43, 46, 47, 58, 59, 60, 61, 62, 67, 71, 72, 73, 77, 80, 85, 88, 92, 93, 94, 101, 102, 103, 104, 107, 108, 109, 110, 118, 122, 123, 124, 127, 130, 133, 137, 143, 144, 145, 148, 149, 150, 151, 152, 160, 161, 162, 163, 164, 167, 170, 171, 172 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Complement of A147820. - Omar E. Pol, Nov 17 2008

m is in the sequence iff A177961(m)<m. - Vladimir Shevelev, May 16 2010

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1)=13 is the first number satisfying simultaneously the two rules.

MATHEMATICA

Select[ Range[300], !PrimeQ[2# + 1] && !PrimeQ[2# - 1] &] (* Robert G. Wilson v, Apr 18 2005 *)

Select[Range[300], NoneTrue[2#+{1, -1}, PrimeQ]&] (* The program uses the NoneTrue function from Mathematica version 10 *)  (* Harvey P. Dale, Jul 07 2015 *)

PROG

(Haskell)

a104278 n = a104278_list !! (n-1)

a104278_list = [m | m <- [1..],

                    a010051' (2 * m - 1) == 0 && a010051' (2 * m + 1) == 0]

-- Reinhard Zumkeller, Aug 04 2015

CROSSREFS

Cf. A040040, A147820.

Cf. A010051, A002808, A099047.

Sequence in context: A145483 A125262 A163754 * A129070 A335036 A307880

Adjacent sequences:  A104275 A104276 A104277 * A104279 A104280 A104281

KEYWORD

easy,nonn

AUTHOR

Alexandre Wajnberg, Apr 17 2005

EXTENSIONS

More terms from Robert G. Wilson v, Apr 18 2005

STATUS

approved

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Last modified June 5 15:37 EDT 2020. Contains 334852 sequences. (Running on oeis4.)