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a(a(n))=n, a self-inverse permutation of natural numbers;
a(n)=n for single primes (A007510) and products of twin prime pairs (A037074).
Table of n, a(n) for n=1..66.
Index entries for sequences that are permutations of the natural numbers
Multiplicative with a(p) = (if p<=3 then p else (if p+2 is prime then p+2 else (if p-2 is prime then p-2 else p))), p prime.
Cf. A072027, A001359, A006512, A072028, A072029, A061898, A064505.
Sequence in context: A092842 A072028 A269377 * A235199 A270426 A270425
Adjacent sequences: A072023 A072024 A072025 * A072027 A072028 A072029
Reinhard Zumkeller, Jun 07 2002