# beginner needs help with sieve program

Maurice Castro maurice@REDACTED
Mon Sep 4 02:00:08 CEST 2000

```The Erastoshenes prime number sieve is an excelent starting problem for
Erlang ... in fact I set it as an exercise in my book. A sample solution
is provided.

http://www.serc.rmit.edu.au/~maurice/erlbk/
http://www.serc.rmit.edu.au/~maurice/erlbk/eg/choice/erasto.erl

This example delibarately does not use: funs, and many of the functions
provided in the modules. Although the provided functions are often
more efficient, they tend to distract from the learning process.

It turns out that it is the remove multiples routine that is at
already established this. My theory is that the problem is actually a problem
in the
algorithm not in the Erlang implemenation as the immediate cause of the
problem is that remove multiples attempts to evaluate over the following
arguments:

T = [2197, 2201, 2203 | ...]
H = 2183
Next = 2184
Num = 13

The algorithm is `unlucky' here as the value of H is exactly 13 more than
the value next. Hence the logic of the algorithm lets you down.

Maurice Castro

```