a0+a1+a2+a3+...+an=C(n,0)+C(n,1)+C(n,2)+C(n,3)+...+C(n,n)
=1+n/1+n(n-1)/(1*2)+n(n-1)(n-2)/(1*2*3)+...+n(n-1)(n-2).1/(1*2*3*...*n)
=2^n

a1+a3+a5+a7+a9=C(10,1)+C(10,3)+C(10,5)+C(10,7)+C(10,9)=2C(10,1)+2C(10,3)+C(10,5)
=2*10+2*10*9*8/(1*2*3)+10*9*8*7*6/(1*2*3*4*5)=20+240+252=512
{最简单的做法是奇数项的和等于偶数项的和}

a0+an=1+1=2