Error: Attempted to access N(2); index out of bounds because numel(N)=1

function results=decay_a2b2c(half_lives,N0,time_units,time_span)
% Calculate decay constant
lambda=log(2)./half_lives(:);
% Call the ODE45 function
[t,N]=ode45(@decay_rate,[0 time_span],N0); results=[t N];
% Plot results
figure
set(gcf,'color','white') 
set(gca,'Fontsize',12,'Fontweight','bold')
plot(t,N,'Linewidth',2)
grid on
xlabel(['Time(' time_units ')'],'Fontsize',12,'Fontweight','bold') 
ylabel('N(t)','Fontsize',12,'Fontweight','bold') 
legend('A','B','C',0)
title_a=['t_{1/2,A}=' num2str(half_lives(1)) ' ' time_units]; 
title_b=['t_{1/2,B}=' num2str(half_lives(2)) ' ' time_units]; 
title_c=['t_{1/2,C}=' num2str(half_lives(3)) ' ' time_units]; 
title([title_a ', ' title_b ', ' title_c])
  function dNdt=decay_rate(t,N)
          A=[-N(1) 0 0; N(1) -N(2) 0; 0 N(2) 0];
       dNdt(N)=A*lambda;

       end
end

-------

decay_a2b2c(489,6.004E22,'sec',2000)

%