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A sieve was used to generate a list of prime numbers. In order to reduce storage requirements, the information about prime or not prime was stored for 30 integers in each byte.
In each 30 integers, for N >= 1, the numbers that might be prime are
N*30+1,
N*30+7,
N*30+11,
N*30+13,
N*30+17,
N*30+19,
N*30+23,
N*30+29
This means that information about prime or not prime only needs to
occupy 8 bits. A ten byte file would hold prime or not prime for 300
integers.
Enter a positive integer in the form below to find out whether it is
a prime number.