OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from T. D. Noe)
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems: Inversion of Multiplicative Functions (invphi.gp).
Paul Pollack and Carl Pomerance, Square values of Euler's function, Bull. London Math. Soc., Vol. 46, No. 2 (2014), pp. 403-414; alternative link. See section 5.
FORMULA
a(n) = sqrt(A038688(n)).
MATHEMATICA
nn = 40000; t = Select[Union[DivisorSigma[1, Range[nn]]], IntegerQ[Sqrt[#]] &]; t = Sqrt[t]; t = Select[t, # < Sqrt[nn] &]
With[{nn=50000}, Union[Select[Sqrt[DivisorSigma[1, Range[nn]]], IntegerQ[ #] && #<=Sqrt[nn]&]]] (* Harvey P. Dale, Jul 12 2021 *)
PROG
(PARI) lista(kmax) = for(k = 1, kmax, if(invsigmaNum(k^2) > 0, print1(k, ", "))); \\ Amiram Eldar, Aug 12 2024, using Max Alekseyev's invphi.gp
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Sep 04 2013
STATUS
approved