Bash script - int variable in for loop

This is my whole script

#!/bin/bash
num_autocorellation=1
index_min=1
index_max=5000
for first in {1..10000..100}
do
for index in {$index_min..$index_max} 
do
    awk 'NR==FNR{a[$0]++;next}a[$0]-->0' eq3_900_915_dgdg_$first.ndx eq3_900_915_dgdg_$index.ndx | tee eq4_${num_autocorellation}_900_915_dgdg_$index.ndx
done
index_min=$(($index_min+100))
index_max=$(($index_max+100))
num_autocorellation=$(($num_autocorellation+1))
done

I want to have in the beginning in my nested loop something like that

for index in {1..5000} 
do
    awk 'NR==FNR{a[$0]++;next}a[$0]-->0' eq3_900_915_dgdg_1.ndx eq3_900_915_dgdg_$index.ndx | tee eq4_1_900_915_dgdg_$index.ndx
done

Then after this for loop will end I want to have

for index in {100..5100} 
do
    awk 'NR==FNR{a[$0]++;next}a[$0]-->0' eq3_900_915_dgdg_1.ndx eq3_900_915_dgdg_$index.ndx | tee eq4_2_900_915_dgdg_$index.ndx
done

and again again until 10000 in that loop

for first in {1..10000..100}

But I have a problem in this part

for index in {$index_min..$index_max} 

Instead of integer I have in the file something like that

eq4_1_900_905_dgdg_{1..5000}.ndx

but I want to have

eq4_1_900_905_dgdg_1.ndx

So how to put here

for index in {$index_min..$index_max} 

int variables?