%I A002784 M0401 N0154
%S A002784 1,1,1,2,3,1,1,4,5,1,3,1,3,1,1,8,15,3,7,4,5,2,3,3,6,2,3,2,3,1,1,16,19,
%T A002784 7,10,5,15,4,5,7,15,3,7,4,5,2,3,5,13,3,5,4,7,1,3,3,5,2,3,1,3,1,1,32,47,
%U A002784 11,31,14,21,6,15,11,31,7,9,7,12,3,7,12,21,7,15,4,11,4,5,7,15,2,7,4,5
%N A002784 A problem in parity.
%D A002784 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002784 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002784 H. Gupta, On a problem in parity, Indian J. Math., 11 (1969), 157-163. 
               MR0260659
%o A002784 (PARI) a(n)=if(n<1,0,sum(k=1,n,if(gcd(n,k) == 1,((n+k-1)!/(n!*k!))%2)))
%Y A002784 Cf. A050169, A073166.
%Y A002784 Sequence in context: A059247 A023570 A011249 this_sequence A166029 A049278 
               A131739
%Y A002784 Adjacent sequences: A002781 A002782 A002783 this_sequence A002785 A002786 
               A002787
%K A002784 nonn
%O A002784 1,4
%A A002784 N. J. A. Sloane (njas(AT)research.att.com).
%E A002784 PARI code and more terms from Michael Somos, Jul 19 2002