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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
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
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. A145680 (analog with unitary sigma).
Sequence in context: A140432 A240695 A004867 * A298671 A073787 A274028
KEYWORD
nonn,more
AUTHOR
Michel Marcus, Sep 04 2018
STATUS
approved