A378508 Values taken by phi(phi(m)) (A010554).

1, 2, 4, 6, 8, 10, 12, 16, 18, 20, 22, 24, 28, 32, 36, 40, 44, 48, 52, 54, 56, 60, 64, 72, 80, 82, 84, 88, 92, 96, 100, 104, 108, 112, 120, 128, 130, 132, 144, 156, 160, 162, 164, 168, 172, 176, 178, 180, 184, 190, 192, 200, 204, 208, 212, 216, 220, 224, 232, 238, 240, 250, 252, 256, 260, 264, 272, 276, 280, 288, 292, 300, 312, 320, 324, 328, 336, 344, 348, 352, 356, 358, 360, 368, 380, 384, 396, 400

Offset: 1

Author

Amiram Eldar, Nov 29 2024

Keywords

• nonn

Comments

Numbers k such that A378506(k) > 0.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
• David M. Bressoud, A Course in Computational Number Theory (web page), CNT.m, Computational Number Theory Mathematica package.

Crossrefs

Cf. A000010, A010554, A378506.

Subsequence of A002202.

Programs

Mathematica

q[k_] := AnyTrue[PhiInverse[k], PhiMultiplicity[#] > 0 &]; Select[Range[1000], q] (* using David M. Bressoud's CNT.m *)

PARI

is(k) = {my(v = invphi(k)); for(i = 1, #v, if(istotient(v[i]), return(1))); 0;} \\ using Max Alekseyev's invphi.gp