|
|
A106667
|
|
a(n) = 1 if prime(n) + 2 is a prime, a(n) = -1 if prime(n) + 2 is a semiprime, otherwise 0.
|
|
1
|
|
|
-1, 1, 1, -1, 1, -1, 1, -1, -1, 1, -1, -1, 1, 0, -1, -1, 1, 0, -1, 1, 0, 0, -1, -1, 0, 1, 0, 1, -1, -1, -1, -1, 1, -1, 1, 0, -1, 0, -1, 0, 1, -1, 1, 0, 1, -1, -1, 0, 1, 0, -1, 1, 0, -1, -1, -1, 1, 0, 0, 1, 0, -1, -1, 1, 0, -1, 0, -1, 1, 0, -1, -1, 0, 0, -1, 0, -1, 0, -1, -1, 1, 0, 1, 0, 0, -1, -1, 0, 1, 0, -1, -1, -1, -1
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
a(1) = -1 because prime(1) = 2 and 2 + 2 = 4 is a semiprime;
a(2) = 1 because prime(2) = 3 and 3 + 2 = 5 is a prime;
a(14) = 0 because prime(14) = 43 and 43 + 2 = 45 is neither prime nor semiprime.
|
|
MAPLE
|
p:= 1:
for n from 1 to 100 do
p:= nextprime(p);
if isprime(p+2) then A[n]:=1
elif numtheory:-bigomega(p+2)=2 then A[n]:=-1
else A[n]:= 0
fi
od:
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,sign,less
|
|
AUTHOR
|
|
|
EXTENSIONS
|
Corrected, and definition clarified, by Robert Israel, Aug 29 2018
|
|
STATUS
|
approved
|
|
|
|