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