A066899 a(n) = card({k : phi(k) == n (mod k)}).

1, 3, 1, 4, 2, 5, 1, 7, 2, 3, 2, 7, 2, 5, 2, 7, 2, 5, 2, 10, 2, 3, 3, 15, 2, 3, 2, 5, 3, 3, 1, 12, 4, 5, 2, 9, 2, 7, 2, 12, 3, 7, 2, 8, 4, 3, 2, 16, 2, 5, 3, 4, 4, 9, 2, 10, 2, 3, 4, 12, 2, 5, 2, 15, 3, 3, 2, 9, 5, 5, 2, 20, 2, 5, 3, 8, 3, 5, 2, 15, 2, 3, 5, 12, 2

Offset

1,2

Comments

Note that k=1 is excluded from the count. - Michel Marcus, Feb 22 2021

Links

Table of n, a(n) for n=1..85.

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems: invphi.gp, 2005-2019.

Prog

(PARI) a(n) = {my(v = invphi(n), m = if (#v, vecmax(v), n)); sum(i=2, m, Mod(eulerphi(i), i) == n); } \\ Michel Marcus, Feb 22 2021; needs invphi.gp

Crossrefs

Cf. A000010, A014197, A066900.

Sequence in context: A066728 A279161 A222046 * A309636 A309650 A139432

Adjacent sequences: A066896 A066897 A066898 * A066900 A066901 A066902

Keyword

nonn

Author

Benoit Cloitre, Jan 24 2002

Extensions

More terms from Michel Marcus, Feb 22 2021

Status

approved