#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11131485
use warnings;

@ARGV = 'd.11131485'; # FIXME used for testing

my %seen;
while( <> )
  {
  my ($r_name, $seq) = (split /\t/)[0, 9];
  $seq =~ s/.{20}\K.*//;
  $seen{"$r_name\t$seq"}++ and print "$r_name\n";
  }
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Works with the data file I had to fake up because you did not provide a sample data file.