%I A079260
%S A079260 0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
%T A079260 0,1,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,
%U A079260 0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0
%N A079260 Characteristic function of primes of form 4n+1 (1 if n is prime of form 
               4n+1, 0 otherwise).
%C A079260 Let M(n) denote the n X n matrix m(i,j)=0 if n divides ij-1, m(i,j) = 
               1 otherwise then det(M(n))=-1 if and only if n =2 or if n is prime 
               ==1 (mod 4).
%C A079260 a(A002144(n)) = 1; a(A137409(n)) = 0. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), 
               Oct 11 2008]
%H A079260 <a href="Sindx_Ch.html#char_fns">Index entries for characteristic functions</
               a>
%o A079260 (PARI) { a(n)=if(n%4==1,isprime(n)) }; vector(100,n,a(n))
%Y A079260 Cf. A002144.
%Y A079260 Sequence in context: A011666 A011669 A023971 this_sequence A025457 A093957 
               A144601
%Y A079260 Adjacent sequences: A079257 A079258 A079259 this_sequence A079261 A079262 
               A079263
%K A079260 nonn
%O A079260 1,1
%A A079260 Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 04 2003