FWIW: Yet another snippet, slightly different approach: 
>perl -wMstrict -le
"sub T {
  my $n = 0;
  $n += $_ for @_;
  return $n <= 9 ? $n : T(split '', $n);
  }
 printf qq{%5s -> %d \n}, $_, T($_) for @ARGV
"
1818  1819 1918  1500 5001 51  2300 0230 32
1 9 0 00 00000 10000 00001
 1818 -> 9
 1819 -> 1
 1918 -> 1
 1500 -> 6
 5001 -> 6
   51 -> 6
 2300 -> 5
 0230 -> 5
   32 -> 5
    1 -> 1
    9 -> 9
    0 -> 0
   00 -> 0
00000 -> 0
10000 -> 1
00001 -> 1

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In reply to Re^2: Question on Recursion by AnomalousMonk
in thread Question on Recursion by prasadbabu

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