login
Smallest prime p not occurring earlier such that p+n is a square, or 0 if no such p exists.
1

%I #4 Dec 05 2013 19:55:38

%S 3,2,13,5,11,19,29,17,7,71,53,37,23,67,181,0,47,31,557,61,43,59,41,97,

%T 0,199,73,197,167,139,113,89,163,191,109,0,107,83,157,401,103,79,101,

%U 317,151,179,149,241,0,239,349,173,271,307,269,233,619,383,137,229

%N Smallest prime p not occurring earlier such that p+n is a square, or 0 if no such p exists.

%C a(n)=0 for square n. - _Ralf Stephan_, Mar 30 2003

%o (PARI) v=vector(1000000):for(n=1,100,f=0:forprime(p=2,1000000,if(!v[p]&&issquare(p+n),f=p:break)): if(f,print1(f","):v[f]=1,print1("0,")))

%Y Cf. A075555, A075557.

%K nonn

%O 1,1

%A _Amarnath Murthy_, Sep 23 2002

%E More terms from _Ralf Stephan_, Mar 30 2003