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A072356 a(n) = if n=p*q^2 for primes p<>q then q*p^2 else n. 1
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 18, 13, 14, 15, 16, 17, 12, 19, 50, 21, 22, 23, 24, 25, 26, 27, 98, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 242, 75, 46, 47, 48, 49, 20, 51, 338, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 147, 64, 65, 66, 67, 578, 69, 70, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(a(n))=n: a self-inverse permutation of natural numbers.

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000

Index entries for sequences that are permutations of the natural numbers

MAPLE

N:= 100: # to get a(1) to a(N)

Ps:= select(isprime, [$1..N/2]):

Qs:= select(`<=`, Ps, floor(sqrt(N/2))):

A:= <($1..N)>:

for p in Ps do

  for q in Qs do

    if p*q^2 <= N then A[p*q^2]:= q*p^2 fi

  od

od:

convert(A, list); # Robert Israel, Mar 08 2016

MATHEMATICA

Table[If[Sort[(ar = Transpose[FactorInteger[n]])[[2]]] == {1, 2}, Times @@ (Reverse[ar[[1]]]^ar[[2]]), n], {n, 71}] (* Ivan Neretin, Jul 09 2015 *)

CROSSREFS

Cf. A054753.

Sequence in context: A004840 A254650 A032994 * A105119 A069799 A225891

Adjacent sequences:  A072353 A072354 A072355 * A072357 A072358 A072359

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jul 18 2002

STATUS

approved

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Last modified January 18 23:05 EST 2019. Contains 319282 sequences. (Running on oeis4.)