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1,2
a(a(n))=n, a self-inverse permutation of natural numbers.
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 mod 4 = 1 and p+2 is prime then p+2 else (if p mod 4 = 3 and p-2 is prime then p-2 else p)), p prime.
a(65) = a(5*13) = a(5)*a(13) = a(4*1+1)*a(13) = (4*1+3)*13 = 7*13 = 91.
Cf. A072029, A071695, A071696, A072026, A072027, A061898, A064505.
Sequence in context: A201543 A073666 A092842 * A269377 A072026 A235199
Adjacent sequences: A072025 A072026 A072027 * A072029 A072030 A072031
nonn,mult
Reinhard Zumkeller, Jun 07 2002
approved