A104278 Numbers n such that 2n+1 and 2n-1 are not primes.

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

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: A349978 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