

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
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OFFSET

1,2


COMMENTS

a(a(n))=n: a selfinverse 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



