A058979 - OEIS

A058979

Number of numbers m such that phi(m) = 4n.

4, 5, 6, 6, 5, 10, 2, 7, 8, 9, 3, 11, 2, 3, 9, 8, 0, 17, 0, 10, 6, 6, 3, 17, 4, 3, 9, 6, 3, 17, 0, 9, 7, 2, 3, 21, 2, 0, 7, 12, 3, 12, 2, 8, 10, 4, 0, 21, 2, 8, 3, 4, 3, 19, 5, 8, 2, 6, 0, 31, 0, 0, 9, 10, 3, 10, 2, 5, 9, 8, 0, 28, 2, 3, 5, 0, 0, 16, 2, 16, 8, 4, 3, 18, 0, 3, 6, 12, 3, 25, 0, 5, 2, 0

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OFFSET

1,1

COMMENTS

Size of invphi(4n) solution-set.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

FORMULA

a(n) = A014197(4*n). - Amiram Eldar, Dec 10 2024

EXAMPLE

For n = 12: 4*n = 48, invphi(48) has 11 solutions: {65,104,105,112,130,140,144,156,168,180,210}, so a(12) = 11.