Re: prime numbers and African artifact

Volker Hetzer (vhe@informatik.tu-chemnitz.de)
12 Jul 95 15:11:37 GMT

nickb@harlequin.co.uk (Nick Barnes) writes:

:In article <rfJ0meEYsDj7075yn@fox.nstn.ns.ca> doldridg@fox.nstn.ns.ca
:(Dave Oldridge) succumbs to a troll and attempts to describe the sieve
:of Eratosthenes:
:start:

:1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

:start at the second pebble and remove every 2nd pebble:

:1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

:start at the 3rd pebble and remove every 3rd pebble (watch carefully):

:1 3 7 9 13 15 19 21 25 27 31 33 37 39 43 45 49 51 55 57 61 63 67 69 73 75

:start at the, erm, 7th pebble and remove every 7th pebble:

:1 3 7 9 13 15 21 25 27 31 33 37 43 45 49 51 55 57 63 67 69 73 75

:etc, leaving you with this:

:1 3 7 9 13 15 21 25 31 33 37 43 49 51 63 67 69 73 75
Yeah, but shouldn't the sieve produce primes?
9,15,21,25,27,33,49,51,63,69,75 are no primes.

See you!
Volker