@_ = (83, 27, 81, 64, 73, 46, 63, 52, 77, 93, 72, 23, 43, 37, 7, 16, 40, 89, 15, 6, 26, 98, 4, 97, 31);

##</code><code>##

sub _{$s += ++$n * ord for @_; $n %= @I; $s %= $X};

##</code><code>##

97*1 + 98*2 + 99*3 = 590

##</code><code>##

$_/=$_ for @_ = 1..$_I%34; 

##</code><code>##

@_ = (1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1);

##</code><code>##

@I[@_] = eeeeeeeeeeeeeeeeeeeeeeeee

##</code><code>##

Iteration 1: @_ = (1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2)

##</code><code>##

@I[@_] = eaaaaaaaaaaaaaaaaaaaaaaaa

##</code><code>##

Iteration 2:
  @_ = (3, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4)
  @I[@_] = vaeeeeeeeeeeeeeeeeeeeeeee

##</code><code>##

Iteration 0:
  @_ = (1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)
  @I[@_] = eeeeeeeeeeeeeeeeeeeeeeeee
Iteration 1:
  @_ = (1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2)
  @I[@_] = eaaaaaaaaaaaaaaaaaaaaaaaa
Iteration 2:
  @_ = (3, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4)
  @I[@_] = vaeeeeeeeeeeeeeeeeeeeeeee
Iteration 3:
  @_ = (7, 5, 4, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8)
  @I[@_] = e errrrrrrrrrrrrrrrrrrrrr

...........

Iteration 10:
  @_ = (23, 14, 78, 94, 68, 42, 58, 22, 13, 12, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24)
  @I[@_] = rsr tciu crrrrrrrrrrrrrrr

...........

Iteration 100:
  @_ = (85, 5, 17, 5, 9, 87, 97, 40, 47, 43, 15, 75, 47, 75, 44, 82, 77, 25, 77, 13, 85, 60, 37, 10, 9)
  @I[@_] = P i o rlr hurus tit PePbo

............

Iteration 1000:
  @_ = (15, 9, 59, 68, 84, 96, 78, 8, 35, 63, 76, 34, 39, 87, 79, 20, 41, 56, 82, 91, 47, 33, 38, 4, 53)
  @I[@_] = hottAorrynsrb o iw ortuen

##</code><code>##

last if $_I == _@I[@_];

##</code><code>##

After calculating of _@I on the line "011":
  $s=19371
  $n=0
Iteration 1:
  $s=6098
  $n=25
Iteration 2:
  $s=12778
  $n=50
Iteration 3:
  $s=7504
  $n=75
Iteration 4:
  $s=32145
  $n=0
Iteration 5:
  $s=43630
  $n=25
Iteration 6:
  $s=16452
  $n=50
Iteration 7:
  $s=5600
  $n=75
Iteration 8:
  $s=27784
  $n=0
Iteration 9:
  $s=15712
  $n=25
Iteration 10:
  $s=28150
  $n=50
Iteration 11:
  $s=26454
  $n=75
................
Iteration 101:
  $s=19938
  $n=25
................
Iteration 1001:
  $s=31849
  $n=25

Just before JAPH-string was printed:
  $s=19371
  $n=0