A121287 - OEIS

%I #14 Jun 07 2019 01:55:19

%S 1,6,60,140,8190,32760

%N Numbers such that Sigma(n)*UnitarySigma(n) is divisible by UnitaryPhi(n)*n.

%C No more terms up to 10^8. - _Michel Marcus_, Jan 24 2019

%C a(7) > 10^12, if it exists. - _Giovanni Resta_, Jun 07 2019

%F {n: (n*A047994(n)) | (sigma(n)*A034448(n)) }.

%o (PARI) uphi(n) = my(f=factor(n)~); prod(i=1, #f, f[1, i]^f[2, i]-1); \\ A047994

%o usigma(n) = sumdivmult(n, d, if(gcd(d, n/d)==1, d)); \\ A034448

%o isok(n) = ((sigma(n)*usigma(n)) % (n*uphi(n))) == 0; \\ _Michel Marcus_, Jan 24 2019

%Y Cf. A000203, A034448, A047994, A121288.

%K nonn,more

%O 1,2

%A _Yasutoshi Kohmoto_, Sep 05 2006