Eratosthenes: 276 BC

Constructs the first prime number sieve. An elegant filter to sift out primes.

1x
2--2
3---3
4x
5----5
6xy
7------7
8x
9y
10xz
11-------11
12yx
13---------13
14xw
15yz
16x
17-----------17
18xy
19-------------19
20xz
21ywu
22x
23----------------23
24xy
25z
26xv
26y
28xw
29--------------------29
30xyz

Very mechanical, works great. Once a list of primes say up to a 1000 are generated, primes can be easily checked on the order of 1,000,000.

Gauss, Euler and others would calculate patches of primes on the order of 1,000,000 in 15 minutes, no tv.

Animation

Eratosthenes also made a surprisingly accurate measurement of the circumference of the Earth. Unrelated to our story.

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