定义数列﹛an﹜：a1=3/2,﹙an=a﹙n-1﹚+n-1n为奇数,3a﹙n-1﹚n为偶数﹚

a(1)=3/2
a(2n)=3a(2n-1)
a(2n+1)=a(2n)+2n=3a(2n-1)+2n
a(2n+1)+(n+1)+1/2=3[a(2n-1)+n+1/2]
{b(n)=a(2n-1)+n+1/2}是首项为a(1)+1+1/2=3,公比为3的等比数列.
a(2n-1)+n+1/2=3^(n)
a(2n-1)=3^(n)-n-1/2
a(2n-1)+a(2n)=a(2n-1)+3a(2n-1)=4a(2n-1)=4*3^n-4n-2
s(n)=4[3+3^2+...+3^n]-4[1+2+...+n]-2n
=12[3^n-1]/2-4n(n+1)/2-2n
=6[3^n-1]-2n(n+1)-2n
=6*3^n-6-2n(n+2)
s(2n)=6*9^n-6-4n(2n+2)
s(2(n+1))=6*9^(n+1)-6-4(n+1)(2n+4)

Ⅰ、a2=3a1=9/2
a3=a2+2=13/2
a4=3a3=39/2
Ⅱ、bn=a﹙2n-1）+n+1/2
b1=a1+1+1/2=3
2n+1为奇数
b(n+1)=a﹙2n+1）+n+1+1/2
=a(2n)+2n+n+1+1/2

对Sn不用奇偶讨论
{bn}为等比数列，可知bn=3^n
b1+b2+……+bn=3*（3^n-1)/2
因bn=a﹙2n-1）+n+1/2,得a(2n-1)=bn-n-1/2
且n为偶数时an=3a﹙n-1﹚
则Sn=a1+a2+……+an=a1+3*a1+a2+3*a2+……+an+3*an
=4*（a1+a3+……+a(2n...