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 A072028 Swap twin prime pairs of form (4*k+1,4*k+3) in prime factorization of n. 3
 1, 2, 3, 4, 7, 6, 5, 8, 9, 14, 11, 12, 13, 10, 21, 16, 19, 18, 17, 28, 15, 22, 23, 24, 49, 26, 27, 20, 31, 42, 29, 32, 33, 38, 35, 36, 37, 34, 39, 56, 43, 30, 41, 44, 63, 46, 47, 48, 25, 98, 57, 52, 53, 54, 77, 40, 51, 62, 59, 84, 61, 58, 45, 64, 91, 66 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(a(n))=n, a self-inverse permutation of natural numbers. LINKS FORMULA 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. EXAMPLE a(65) = a(5*13) = a(5)*a(13) = a(4*1+1)*a(13) = (4*1+3)*13 = 7*13 = 91. CROSSREFS Cf. A072029, A071695, A071696, A072026, A072027, A061898, A064505. Sequence in context: A343600 A343601 A331275 * A269377 A072026 A332213 Adjacent sequences:  A072025 A072026 A072027 * A072029 A072030 A072031 KEYWORD nonn,mult AUTHOR Reinhard Zumkeller, Jun 07 2002 STATUS approved

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Last modified July 29 05:30 EDT 2021. Contains 346340 sequences. (Running on oeis4.)