OFFSET
1,2
COMMENTS
Numbers k such that {phi(d) : d|k} = {d : d|(k+1), d<(k+1)} as sets.
Conjecture: last term is 4294967295.
Sequence differs from A203966 because 83623935 is not in this sequence.
EXAMPLE
2 is a term since {phi(d) : d|2} = {1} = {d; d|2, d<2}.
15 is a term since {phi(d) : d|15} = {1, 2, 4, 8} = {d : d|16, d<16}.
PROG
(Magma) [n: n in [1..100000] | Set([EulerPhi(d): d in Divisors(n)]) eq Set([d: d in Divisors(n+1) | d lt n+1 ])]
(PARI) isok(n) = {sphi = []; fordiv(n, d, sphi = Set(concat(sphi, eulerphi(d)))); sphi == setminus(Set(divisors(n+1)), Set(n+1)); } \\ Michel Marcus, Nov 23 2014
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Jaroslav Krizek, Nov 22 2014
EXTENSIONS
Edited and a(7) added by Max Alekseyev, May 04 2024
STATUS
approved