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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

Table of n, a(n) for n=1..66.

Index entries for sequences that are permutations of the natural numbers

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: A201543 A073666 A092842 * A269377 A072026 A235199

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 September 24 22:31 EDT 2017. Contains 292441 sequences.