A073540 Composite numbers k such that k/phi(k) - sigma(k)/k has numerator equal to 1.

4, 6, 8, 9, 16, 24, 25, 27, 28, 32, 40, 49, 64, 81, 121, 125, 128, 169, 224, 243, 256, 289, 343, 360, 361, 496, 512, 529, 625, 672, 729, 841, 864, 936, 961, 1024, 1331, 1369, 1681, 1849, 2016, 2048, 2176, 2187, 2197, 2209, 2401, 2809, 3125, 3481, 3721, 4096

Offset: 1

Author

Benoit Cloitre, Aug 27 2002

Keywords

• easy
• nonn

Links

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

Crossrefs

Cf. A000010, A000203, A017665, A017666, A076512, A109395.

Programs

Mathematica

Select[Range[4100], ! PrimeQ[#] && Numerator[#/EulerPhi[#] - DivisorSigma[1, #]/#] == 1 &] (* Jayanta Basu, Jul 01 2013 *)

PARI

isok(k) = if (!isprime(k), numerator(k/eulerphi(k) - sigma(k)/k) == 1); \\ Michel Marcus, May 10 2022