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, 122993370817276805096761690549125120000, 31, 32, 1205601408000

Offset

2,1

Links

Max Alekseyev, Table of n, a(n) for n = 2..47

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.

a(n) = A319313(2*n). - Max Alekseyev, Oct 20 2025

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

Bisection of A319313.

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

Cf. A030163, A305678.

Cf. A145680 (analog with unitary sigma).

Sequence in context: A140432 A240695 A004867 * A298671 A073787 A382533

Adjacent sequences: A318839 A318840 A318841 * A318843 A318844 A318845

Keyword

nonn

Author

Michel Marcus, Sep 04 2018

Extensions

Terms a(30) onward from Max Alekseyev, Oct 20 2025

Status

approved