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A104278
Numbers m such that 2m+1 and 2m-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
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
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
(PARI) select( {is_A104278(n)=!isprime(2*n-1)&&!isprime(2*n+1)}, [1..222]) \\ M. F. Hasler, Apr 29 2024
CROSSREFS
Intersection of A047845 and A104275.
Sequence in context: A349978 A125262 A163754 * A129070 A335036 A307880
KEYWORD
easy,nonn
AUTHOR
Alexandre Wajnberg, Apr 17 2005
EXTENSIONS
More terms from Robert G. Wilson v, Apr 18 2005
STATUS
approved