OFFSET
1,1
COMMENTS
a(2n+1) = 0 if 4n+3 is composite. Conjecture: There are no other zeros.
LINKS
Robert Israel, Table of n, a(n) for n = 1..20000
MAPLE
for n from 1 to 245 do if(n mod 2 =1 and not isprime(2*n+1)) then a[n]:=0: else i:=1:while(not isprime(n*ithprime(i)+1)) do i:=i+1:od: a[n]:=ithprime(i):fi:od:seq(a[j], j=1..245); # Sascha Kurz, May 09 2004
N:= 1000: # to get a(n) for n <= 2*N
count:= 0:
a:= Vector(2*N):
for i from 1 to 2*N do if isprime(2*i+1) then
a[i]:= 2;
if type(i, even) then count:= count+1 fi
fi od:
for p in select(isprime, [$3..N]) while count < N do
for q in select(isprime, [seq(2*p*i+1, i=1..N)]) do
n:= (q-1)/p;
if a[n] = 0 then a[n]:= p;
count:= count+1;
fi
od
od:
A089367:= [seq(a[i], i=1..2*N)]; # Robert Israel, May 26 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Nov 08 2003
EXTENSIONS
More terms from Sascha Kurz, May 09 2004
STATUS
approved