OFFSET
1,1
LINKS
J. O. M. Pedersen, Known Unitary Sociable Numbers of order different from four [Via Internet Archive Wayback-Machine]
Eric Weisstein's World of Mathematics, Unitary Sociable Numbers
J. O. M. Pedersen, Order 10 cycles
PROG
(PARI) f(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d)) - n;
isok10(n) = iferr(f(f(f(f(f(f(f(f(f(f(n)))))))))) == n, E, 0);
isok5(n) = iferr(f(f(f(f(f(n))))) == n, E, 0);
isok2(n) = iferr(f(f(n)) == n, E, 0);
isok1(n) = iferr(f(n) == n, E, 0);
isok(n) = isok10(n) && !isok1(n) && !isok2(n) && !isok5(n);
CROSSREFS
Cf. A063919 (sum of proper unitary divisors).
KEYWORD
nonn,more
AUTHOR
Michel Marcus, Oct 02 2018
STATUS
approved