%I A001650
%S A001650 1,3,3,3,5,5,5,5,5,7,7,7,7,7,7,7,9,9,9,9,9,9,9,9,9,11,11,11,11,11,11,11,
%T A001650 11,11,11,11,13,13,13,13,13,13,13,13,13,13,13,13,13,15,15,15,15,15,15,
%U A001650 15,15,15,15,15,15,15,15,15,17,17,17,17,17,17,17,17,17,17,17,17,17
%N A001650 n appears n times (n odd).
%C A001650 For n >= 0, a(n+1) is the number of integers x with |x| <= sqrt(n), or 
               equivalently the number of point in the Z^1 lattice of norm <= n+1. 
               - David W. Wilson, Oct 22 2006
%D A001650 J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", 
               Springer-Verlag, p. 106.
%F A001650 a(n) = 1 + 2*floor(sqrt(n-1)), n > 0. - Antonio Esposito (antonio.b.esposito(AT)italtel.it), 
               Jan 21 2002
%F A001650 G.f.: theta_3(x)*x/(1-x). a(n+1)=a(n)+A000122(n). - Michael Somos, Apr 
               29 2003.
%o A001650 (PARI) a(n)=if(n<1,0,1+2*sqrtint(n-1))
%Y A001650 Cf. A001670. Partial sums of A000122.
%Y A001650 Sequence in context: A136800 A126661 A162226 this_sequence A130175 A101290 
               A080605
%Y A001650 Adjacent sequences: A001647 A001648 A001649 this_sequence A001651 A001652 
               A001653
%K A001650 nonn,easy
%O A001650 1,2
%A A001650 N. J. A. Sloane (njas(AT)research.att.com).
%E A001650 More terms from Michael Somos, Apr 29 2003.