The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A127956 Prime numbers p such that (2^p+1)/3 is composite. 12
 29, 37, 41, 47, 53, 59, 67, 71, 73, 83, 89, 97, 103, 107, 109, 113, 131, 137, 139, 149, 151, 157, 163, 173, 179, 181, 193, 197, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 317, 331, 337, 349, 353, 359, 367, 373 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If p-1 is squarefree, 2a(n) is the multiplicative order of 2 modulo every divisor d>1 of (2^p+1)/3. - Vladimir Shevelev, Jul 15 2008 LINKS MATHEMATICA a = {}; Do[c = (2^Prime[x] + 1)/3; If[PrimeQ[c] == False, AppendTo[a, Prime[x]]], {x, 2, 100}]; a Select[Prime[Range[2, 100]], CompositeQ[(2^#+1)/3]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 07 2021 *) CROSSREFS Cf. A000979, A000978, A124400, A126614, A127955, A127957. Sequence in context: A089296 A089297 A250291 * A347038 A166088 A295490 Adjacent sequences:  A127953 A127954 A127955 * A127957 A127958 A127959 KEYWORD nonn AUTHOR Artur Jasinski, Feb 09 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 28 15:04 EDT 2022. Contains 354115 sequences. (Running on oeis4.)