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

1,1

Links

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

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A228020 A163282 A095404 * A123710 A075243 A024370

Adjacent sequences: A073537 A073538 A073539 * A073541 A073542 A073543

Keyword

easy,nonn

Author

Benoit Cloitre, Aug 27 2002

Status

approved