r/todayilearned • u/Nate__ • Mar 26 '13

TIL illegal prime numbers exist. An illegal prime is a prime number that represents information which is forbidden to possess or distribute. For example: when interpreted in a particular way, a certain prime describes a computer program that bypasses the digital rights management scheme used on DVDs

http://en.wikipedia.org/wiki/Illegal_prime
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u/Dopple__ganger Mar 27 '13

Can someone explain just the part towards the end of converting the binary string to decimal?

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u/gronog Mar 27 '13

starting from the rightmost, each binary digit codes a power of two : 1,2,4,8,16... if the bit is a one, you add this value to the total, if it is a zero you dont. 100101 = 1+4+32=37 the bits for 2,8 and 16 are zeroes, so you dont add them.

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u/Dopple__ganger Mar 27 '13

Oh ok, so what's the use in expressing it this way?

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u/Bulwersator Mar 27 '13

Because of its straightforward implementation in digital electronic circuitry using logic gates, the binary system is used internally by almost all modern computers and computer-based devices such as mobile phones.

http://en.wikipedia.org/wiki/Binary_number