OFFSET
1,1
COMMENTS
Sequence is infinite. For instance, it contains 2^m for m not of the form 2^k - 1. - Eric M. Schmidt, Apr 09 2015
LINKS
Eric M. Schmidt, Table of n, a(n) for n = 1..10000
EXAMPLE
Both 16 and 33 = 16*2 + 1 are composite, so 16 is in this sequence.
MATHEMATICA
Select[Range[200], !PrimeQ[#] && !PrimeQ[2 # + 1] &] (* Vincenzo Librandi, Apr 09 2015 *)
Select[Range[200], AllTrue[{#, 2#+1}, CompositeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 12 2019 *)
PROG
(PARI) isA077654(n) = !(isprime(n)) & !(isprime(2*n+1)); \\ Michael B. Porter, Oct 01 2009
(Magma) [n: n in [1..200] | not IsPrime(n) and not IsPrime(2*n+1)]; // Vincenzo Librandi, Apr 09 2015
(Python)
from sympy import isprime
def ok(n): return n >= 4 and not isprime(2*n+1) and not isprime(n)
print(list(filter(ok, range(4, 143)))) # Michael S. Branicky, Apr 10 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Lior Manor, Nov 13 2002
EXTENSIONS
Offset corrected by Eric M. Schmidt, Apr 09 2015
STATUS
approved