|
|
A173136
|
|
Odd nonprimes n such that exactly one of 2n-1 and 2n+1 is prime.
|
|
1
|
|
|
1, 27, 33, 35, 39, 45, 49, 55, 57, 63, 65, 81, 87, 91, 95, 105, 111, 115, 117, 119, 121, 125, 129, 147, 153, 155, 159, 165, 169, 175, 177, 183, 187, 189, 195, 201, 205, 209, 215, 217, 219, 221, 225, 243, 245, 249, 255, 273, 279, 289, 297, 299, 301, 303, 315
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
LINKS
|
|
|
EXAMPLE
|
a(1)=1 because 2*1-1=1 is nonprime and 2*1+1=3 is prime.
|
|
MATHEMATICA
|
Select[Range[1, 341, 2], !PrimeQ[#]&&Total[Boole[PrimeQ[2 #+{1, -1}]]]==1&] (* Harvey P. Dale, Sep 01 2017 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy,less
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|