OFFSET
1,2
COMMENTS
No more terms up to 10^8. - Michel Marcus, Jan 24 2019
a(7) > 10^12, if it exists. - Giovanni Resta, Jun 07 2019
PROG
(PARI) uphi(n) = my(f=factor(n)~); prod(i=1, #f, f[1, i]^f[2, i]-1); \\ A047994
usigma(n) = sumdivmult(n, d, if(gcd(d, n/d)==1, d)); \\ A034448
isok(n) = ((sigma(n)*usigma(n)) % (n*uphi(n))) == 0; \\ Michel Marcus, Jan 24 2019
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Yasutoshi Kohmoto, Sep 05 2006
STATUS
approved