A318842 a(n) is the least integer m such that A047994(m) = ((n-1)/n)*m where A047994 is the unitary totient function, or 0 if there is no such m.

2, 3, 4, 5, 144, 7, 8, 9, 400, 11, 64281600, 13, 84672, 129600, 16, 17, 518400, 19, 4327213363200, 254016, 6326996189184000000, 23, 300174920860041216000, 25, 2747437056, 27, 3136, 29

Offset

2,1

Comments

If it is not 0, a(30) > 10^30. - Michel Marcus, Sep 08 2018

Links

Table of n, a(n) for n=2..29.

Yasutoshi Kohmoto, UnitaryPhi, SeqFan list, Aug 31 2018.

Michel Marcus, solve_uphi pari code

Formula

a(pp) = pp iff pp is a prime power (A000961) > 1.

Prog

(PARI) \\ uses the "solve_uphi pari code", see links
a(n) = {my(lim = 1, v); while (1, v = solve_uphi(n-1, n, lim); if (#v, return (v[1])); lim *= 10; ); }

Crossrefs

Cf. A000961 (primepowers), A047994 (unitary totient).

Cf. A030163, A305678.

Cf. A145680 (analog with unitary sigma).

Sequence in context: A140432 A240695 A004867 * A298671 A073787 A274028

Adjacent sequences: A318839 A318840 A318841 * A318843 A318844 A318845

Keyword

nonn,more

Author

Michel Marcus, Sep 04 2018

Status

approved