I have to do a search for small DNA sequences in the genome of an organism in ENA. I have the accession number and project id. However, I can't download the whole genome because of the download size and would prefer to do it online if possible. I have a rough idea of the part of the genome I wish to scan in, don't know if that's relevant.
While it is much better/easier to download and do the exact search on your own, it is possible to do something similar, online. You can use NCBI-BLAST and increase the word length and mismatch/gap penalty. It also allows restricting the subject space; you can even align two sequences. The BLAST on ENA does not have much flexibility (subject restriction/word length). Perhaps you can look for a duplicate sequence on NCBI.
If this genome is available on UCSC genome browser then you can use BLAT too. However, it only accepts sequences larger than 19nt.