A057826 Greatest number with totient 2n (or zero when no such number exists).

6, 12, 18, 30, 22, 42, 0, 60, 54, 66, 46, 90, 0, 58, 62, 120, 0, 126, 0, 150, 98, 138, 94, 210, 0, 106, 162, 174, 118, 198, 0, 240, 134, 0, 142, 270, 0, 0, 158, 330, 166, 294, 0, 276, 0, 282, 0, 420, 0, 250, 206, 318, 214, 378, 242, 348, 0, 354, 0, 462, 0, 0, 254, 510

Offset

1,1

Comments

If a(n) = 0, n is a nontotient number - see (A005277)/2.

Links

T. D. Noe, Table of n, a(n) for n=1..10000

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

Mathematica

a = Table[0, {100}]; Do[ t = EulerPhi[n]/2; If[t < 101, a[[t]] = n], {n, 1, 10^3}]; a

Prog

(PARI) a(n) = invphiMax(2*n); \\ Amiram Eldar, Nov 11 2024, using Max Alekseyev's invphi.gp

Crossrefs

Bisection of A057635. Cf. A000010, A005277, A002181.

Sequence in context: A350685 A270383 A088345 * A334543 A330853 A268657

Adjacent sequences: A057823 A057824 A057825 * A057827 A057828 A057829

Keyword

nonn

Author

Robert G. Wilson v, Nov 08 2000

Status

approved