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Today is Day 25 of 2015

25

is a centreed octagonal number.
is the smallest square number that can be written as a sum of 2 squares: 52 = 42 + 32

= 1 + 3 + 5 + 7 + 9 (sum of the first five odd numbers)

= (12 + 22)2
= 132 - 122

252 = 72 + 242 (Pythagorean triple)

4! + 1 = 25

25% = 1/4

When you add the digit 6 to 25 you obtain two squares:
625 = 252, and 256 = 162

We can readily test for divisibility by 25 by seeing if the last two digits of the number match 25, 50, 75 or 00.

It seems that 25 and 27 are the only case of a square and a cube separated by 2 (can you prove it?).

"The two greatest highway menaces are drivers under 25 going over 65 and drivers over 65 going under 25".

The 25th Hour is a 2002 Spike Lee urban drama based on David Benioff's novel.

Many thanks are extended to Archimedes' Lab for their information.




25

Today is day number   of 2015. Below are various representations of the number 25, some dating thousands of years, and some very modern.

Chinese

Egyptian

Mayan

 

Babylonian

Greek

Abacus

Roman

 

Hex

 

Binary

 

Many thanks are extended to Jo Edkins for her wonderful work.

 

 



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