First off, arrays have a 0-based index. For example:

my @array = 1..10;
print "Index 7 (before):  $array[7]\n";
print "Index 8 (before):  $array[8]\n";
$array[7] = $array[7] . $array[8];
print "Index 7 (after):  $array[7]\n";
print "Index 8 (after):  $array[8]\n";
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Would yield:

Index 7 (before): 8
Index 8 (before): 9
Index 7 (after): 89
Index 8 (after): 9
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If you want to have an element disappear when concatenated elsewhere, you could use splice:

$array[7] = $array[7] . splice @array, 8, 1;
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Your method:   1 2 3 4 5 6 7 89 9 10
Splice method: 1 2 3 4 5 6 7 89   10
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