All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars
 perplexus dot info

 Non - Zero Digit (Posted on 2003-12-21)
What is the last non - zero digit in (20!)!? (That is, factorial of 20 factorial).

 See The Solution Submitted by Ravi Raja Rating: 2.6667 (6 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
 re: simple solution | Comment 6 of 11 |
(In reply to simple solution by Tristan)

"making x!'s last nonzero digit repeat every 40"

The last non-zero digit does not repeat every 40.

Here are the last digits of the factorials of the first few multiples of 40:

```
40      2

80      8

120     6

160     6

200     2

240     6

280     4

320     4

360     6

400     8

440     2

480     6

520     6

560     4

600     6

640     8

680     4

720     6

760     4

800     6

840     6

880     6

920     8

960     6

1000    2

1040    4

1080    6

1120    2

1160    8

1200    6

1240    8

1280    6

1320    6

1360    4

1400    4

1440    6

1480    8

1520    4

1560    6

1600    4

```

--------
For the first couple,

40! = 815915283247897734345611269596115894272000000000
80! = 71569457046263802294811533723186532165584657342365752577109445058227039255480148842668944867280814080000000000000000000
 Posted by Charlie on 2003-12-22 08:43:51

 Search: Search body:
Forums (0)