Factorials

0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
10! = 3628800
11! = 39916800 ........ 66 weeks
12! = 479001600 ....... 792 weeks (792 / 66 = 12 )
13! = 6227020800 ...... 10296 weeks (10296 / 792 = 13)
14! = 87178291200 ...... 144144 weeks (144144 / 10296 = 14 )
15! = 1307674368000
16! = 20922789888000
17! = 355687428096000
18! = 6402373705728000
19! = 121645100408832000
20! = 2432902008176640000
21! = 51090942171709440000

1 hour = 3600 seconds
1 day = 86400 seconds
1 week = 604800 seconds .... 6 weeks = 604800 * 6 = 3628800 = 10!
1 year = 31556926 seconds ... 11! is larger than the number of seconds in a year
[ 39916800 - 31556926 = 8359874 seconds or 96.75780092592592 days]

31556926 * 12 = 378683112
12! is larger than the number of seconds in 12 years
13! is larger than the number of seconds in a century.

5! - 4! = 96 seconds
6! - 5! = 600 seconds
7! - 6! = 4320 seconds = 0.05 Days
8! - 7! = 35280 seconds = 0.4083333333333333 Days
9! - 8! = 322560 seconds = 3.7333333333333334 Days = 0.533333333 week
10! - 9! = 3265920 seconds = = 37.8 Days = 5.4 weeks
11! - 10! = 36288000 seconds = 420 days = 60 weeks

1! + 2! = 3

1! + 2! + 3! = 9

1! + 2! + 3! + 4! = 33

1! + 2! + 3! + 4! + 5! = 153

1! + 2! + 3! + 4! + 5! + 6! = 873

1! + 2! + 3! + 4! + 5! + 6! + 7! = 5913

1! + 2! + 3! + 4! + 5! + 6! + 7! + 8! = 46233

1! + 2! + 3! + 4! + 5! + 6! + 7! + 8! + 9! = 409113 (0.676443452 week)

1! + 2! + 3! + 4! + 5! + 6! + 7! + 8! + 9! + 10! = 4037913 (6.676443452 weeks)