How to sort array like this?

Dear all expert programmers,
Please help me for sorting array like this

a(1)=20
a(2)=99
a(3)=85
a(4)=30
a(5)=1

I want result to show below
2=99
3=85
4=30
1=20
5=1

First digit mean index of array.

Thank you for all post.