OFFSET
1,2
COMMENTS
From Robert Israel, Mar 20 2018: (Start)
If m and n are coprime members of the sequence, then m*n is in the sequence.
Includes all numbers of the forms p^(4*i*(i+1)) and p^(2*i)*q^(2*i) where p, q are distinct primes and i is a positive integer. (End)
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A063774(n)^2. - Leroy Quet, May 16 2010
MAPLE
with(numtheory): a := proc (n) if type(sqrt(tau(n^2)), integer) = true then n^2 else end if end proc: seq(a(n), n = 1 .. 130); # Emeric Deutsch, May 11 2010
MATHEMATICA
Select[Range[150], IntegerQ[Sqrt[DivisorSigma[0, #^2]]]&]^2 (* Vincenzo Librandi, Mar 21 2018 *)
PROG
(PARI) isok(n) = issquare(n) && issquare(numdiv(n)); \\ Michel Marcus, Mar 21 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Apr 27 2010
EXTENSIONS
Extended by Emeric Deutsch and Jon E. Schoenfield, May 11 2010
STATUS
approved