Kata

I have two questions about permutation task as following:

1. In test case, [10] should return 0. However, 0! and 1! are 1 in math.
2. In test case, [1,...,13] should return 67xxxxxxx . However, 13! is 6227020800 in math.

So is it permutation task different to the math formular? is it the new definition by kata? If this permutation definted by kata, please let me know how [1,....,13] in test case got 67xxxxxxx. I don't need code but fomular please. Thanks.

I am new here. Please let me know how to submit my solution. Many thanks!

Passed all tests before 30 to 50 cases, then failed all tests after.

 Testing for iterable: iayciemrkxpuzihjretxqhcptrrkfxlvswlpnodjnwajgmbslg------------>  counter:31035053229546175414930574765053879335254564565067479107390930944
31035053229546199656252032972759319953190362094566672920420940312L should equal 31035053229546175414930574765053879335254564565067479107390930944L
 Testing for iterable: [87, 83, 12, 90, 18, 118, 50, 125, 95, 133, 41, 70, 11, 106, 104, 23, 32, 5, 27, 53, 144, 54, 52, 24, 88, 85, 16, 33, 134, 135]------------>  counter:274410818470141979392411550351360
274410818470142134209703780940312L should equal 274410818470141979392411550351360L

...
...

 Testing for iterable: [496, 36, 47, 319, 214, 461, 404, 410, 424, 437, 196, 199, 125, 306, 372, 280, 517, 324, 132, 204, 531, 512, 284, 399, 207, 118, 158, 264, 185, 343, 91, 93, 331, 43, 335, 112, 356, 547, 394, 135, 477, 49, 179, 401, 511, 307, 130, 532, 312, 183, 352, 149, 51, 460, 127, 291, 459, 299, 290, 143, 111, 305, 246, 92, 266, 42, 533, 542, 400, 374, 106, 490, 342, 421, 363, 282, 154, 63, 83, 539, 124, 23, 74, 22, 478, 100, 228, 402, 332, 380, 314, 538, 520, 325, 425, 60, 482, 87, 535, 186, 194, 311, 488, 78, 486, 470, 491, 259, 24, 417]------------>  counter:16028178396288989057245308390927932465331623439654827235469952068851902112396223421767896724456884403833923460385593556416659605999580930976124053379571847909205421911042378694656
16028178396289014701258409855092678943673045433708423928570406360980746444276798572896043427681153914716768010060384387640448280252480370395985821340917452556442336528920420940312L should equal 16028178396288989057245308390927932465331623439654827235469952068851902112396223421767896724456884403833923460385593556416659605999580930976124053379571847909205421911042378694656L

Passed all up to 10 elements cases so i guess i got the correct pattern, which is weird that results are slightly different because it's just integer calculation. So what could the problem be....