If possible, the best solution is to calculate your decimal numbers from integer numbers and not from other decimal numbers. This prevents an accumulation of error. If you case, this is possible.

$bu[0] = 0;
for my $i (1 .. 2*$nb) {    # Easier to read. Just as efficient.
    $bu[$i] = $i * $beu;    # Fix.
    print "$i\t$bu[$i]\n";
}
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