Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #13 Dec 11 2019 05:05:05
%S 1,2,3,6,14,15,30,35,42,70,78,105,190,210,348,357,418,570,714,910,
%T 1045,1144,1254,2090,2296,2730,3135,3432,4060,4522,4674,5278,6270,
%U 6888,10168,10659,10824,12180,12441,13566,14630,15834,16770,17160
%N Numbers such that sigma(n)^2 is divisible by UnitarySigma(n)*UnitaryPhi(n).
%H Donovan Johnson, <a href="/A121556/b121556.txt">Table of n, a(n) for n = 1..1000</a>
%p for n from 1 to 20000 do if numtheory[sigma](n)^2 mod (A047994(n)*A034448(n)) = 0 then printf("%d,",n) ; end if;end do:
%t f[p_, e_] := (p^(e+1)-1)^2/(p-1)^2/(p^(2*e)-1); seqQ[1] = True; seqQ[n_] := IntegerQ [Times @@ (f @@@ FactorInteger[n])]; Select[Range[17160], seqQ] (* _Amiram Eldar_, Dec 11 2019 *)
%Y Cf. A000203, A121647, A078557, A020492, A034448, A047994.
%K nonn
%O 1,2
%A _Yasutoshi Kohmoto_, Sep 12 2006