This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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