A160597 Denominator of coresilience C(n) = (n - phi(n))/(n-1).

1, 2, 3, 4, 5, 6, 7, 8, 3, 10, 11, 12, 13, 2, 15, 16, 17, 18, 19, 20, 7, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 11, 34, 35, 36, 37, 38, 13, 40, 41, 42, 43, 44, 15, 46, 47, 48, 49, 50, 51, 52, 53, 18, 55, 8, 19, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 3, 70, 71, 72, 73, 74

Offset: 2

Author

M. F. Hasler, May 23 2009

Keywords

• nonn
• frac
• look

Comments

Obviously C(p) = 1/(p-1) for all primes p.

Examples

			a(10)=3 since for n=10, we have (n - phi(n))/(n-1) = (10-4)/9 = 2/3.
		

Links

• Robert Israel, Table of n, a(n) for n = 2..10000
• Project Euler, Problem 245: resilient fractions, May 2009

Crossrefs

Cf. A160598.

Programs

Magma

[Denominator((n-EulerPhi(n))/(n-1)): n in [2..80]]; // Vincenzo Librandi, Dec 27 2016

Maple

seq(denom((n-numtheory:-phi(n))/(n-1)),n=2..100); # Robert Israel, Dec 26 2016

Mathematica

Denominator[Table[(n - EulerPhi[n])/(n - 1), {n, 2, 20}]] (* G. C. Greubel, Dec 26 2016 *)

PARI

A160597(n)=denominator((n-eulerphi(n))/(n-1))