Primefree sequences

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A primefree sequence is a sequence whose terms are never prime, but in a nontrivial way.

For example, a Fibonacci-like sequence

a (0) = a0; a (1) = a1; a (n) = a (n  − 1) + a (n  − 2), n   ≥   2

, where

a0

and

a1

are coprime and whose terms are [surprisingly!] never prime. (See Fibonacci-like primefree sequences.)

External links

• Weisstein, Eric W., Primefree Sequence, from MathWorld—A Wolfram Web Resource.