A378637 Largest m <= n such that phi(m) divides n, where phi is the Euler totient function (A000010).

1, 2, 2, 4, 2, 6, 2, 8, 2, 6, 2, 12, 2, 6, 2, 16, 2, 18, 2, 12, 2, 6, 2, 24, 2, 6, 2, 12, 2, 22, 2, 32, 2, 6, 2, 36, 2, 6, 2, 33, 2, 18, 2, 23, 2, 6, 2, 48, 2, 22, 2, 12, 2, 54, 2, 30, 2, 6, 2, 50, 2, 6, 2, 64, 2, 46, 2, 12, 2, 22, 2, 72, 2, 6, 2, 12, 2, 18, 2, 75

Offset

1,2

Links

Paolo Xausa, Table of n, a(n) for n = 1..10000

Formula

a(2*k+1) = 2, for k >= 1.

Mathematica

A378637[n_] := If[OddQ[n] && n > 2, 2, Module[{m = n}, While[!Divisible[n, EulerPhi[m]], m--]; m]];
Array[A378637, 100]

Prog

(PARI) a(n) = my(m=n); while (n % eulerphi(m), m--); m; \\ Michel Marcus, Dec 05 2024

Crossrefs

Right border of A378636.

Cf. A000010, A319048, A378641.

Sequence in context: A080221 A137849 A316440 * A118982 A129457 A275365

Adjacent sequences: A378634 A378635 A378636 * A378638 A378639 A378640

Keyword

nonn,easy,new

Author

Paolo Xausa, Dec 03 2024

Status

approved