|
|
A230039
|
|
Primes p such that 2*p+1 is not prime and 2*p+3 is prime.
|
|
3
|
|
|
7, 13, 17, 19, 43, 47, 67, 73, 97, 127, 137, 139, 157, 167, 193, 197, 199, 223, 227, 229, 269, 277, 283, 307, 337, 349, 353, 379, 383, 397, 409, 439, 463, 467, 487, 503, 523, 547, 557, 563, 599, 607, 613, 617, 643, 647, 739, 773, 797, 827, 853, 859, 887, 929
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
|
|
LINKS
|
|
|
EXAMPLE
|
43 is in the sequence because 2*43+1=87 (not prime) and 2*43+3=89 (prime).
|
|
MATHEMATICA
|
Select[Range[10^5], PrimeQ[#]&& !PrimeQ[2#+1]&& PrimeQ[2#+3]&]
|
|
PROG
|
(Magma) [p: p in PrimesUpTo(2500)|not IsPrime(2*p+1) and IsPrime(2*p+3)];
(PARI) is(n) = ispseudoprime(n) && !ispseudoprime(2*n+1) && ispseudoprime(2*n+3) \\ Felix Fröhlich, Jan 14 2017
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|