

A251561


A permutation of the natural numbers: interchange p and 2p for every prime p.


3



1, 4, 6, 2, 10, 3, 14, 8, 9, 5, 22, 12, 26, 7, 15, 16, 34, 18, 38, 20, 21, 11, 46, 24, 25, 13, 27, 28, 58, 30, 62, 32, 33, 17, 35, 36, 74, 19, 39, 40, 82, 42, 86, 44, 45, 23, 94, 48, 49, 50, 51, 52, 106, 54, 55, 56, 57, 29, 118, 60, 122, 31, 63, 64, 65, 66
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OFFSET

1,2


COMMENTS



LINKS



MATHEMATICA

a251561[n_] := Block[{f}, f[x_] := Which[PrimeQ[x], 2 x, PrimeQ[x/2], x/2, True, x]; Array[f, n]]; a251561[66] (* Michael De Vlieger, Dec 26 2014 *)


PROG

(Python)
from sympy import isprime
....if n == 2:
........return 4
....q, r = divmod(n, 2)
....if r :
........if isprime(n):
............return 2*n
........return n
....if isprime(q):
........return q
(Haskell)
a251561 1 = 1
a251561 n  q == 1 = 2 * p
 p == 2 && a010051' q == 1 = q
 otherwise = n
where q = div n p; p = a020639 n


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



