I am trying to download some fastq files from ENA and would like to do a loop for my commands. 

```
for (( i = 36; i <= 43; i++ ))

do

wget ftp.sra.ebi.ac.uk/vol1/fastq/SRR705/006/SRR70591$i/SRR70591$i_1.fastq.gz ftp.sra.ebi.ac.uk/vol1/fastq/SRR705/006/SRR70591$i/SRR70591$i_2.fastq.gz

done

```

and the output was this 

```
--2018-08-19 22:37:14--  http://ftp.sra.ebi.ac.uk/vol1/fastq/SRR705/006/SRR7059137/SRR70591.fastq.gz
Resolving ftp.sra.ebi.ac.uk (ftp.sra.ebi.ac.uk)... 193.62.192.7
Connecting to ftp.sra.ebi.ac.uk (ftp.sra.ebi.ac.uk)|193.62.192.7|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2018-08-19 22:37:14 ERROR 404: Not Found.

```

Notably the error occured because

"`37_1`" is missing from the output `SRR70591.fastq.gz`. 

I've tried various iterations of the, and found out that the command does not work well if underscore"`_`" goes directly after "`$i`" command.
Do you guys have any insights into how I can change the command to make it work? 

Thanks guys