A073757 a(n) = d(n) + phi(n) - 1.

1, 2, 3, 4, 5, 5, 7, 7, 8, 7, 11, 9, 13, 9, 11, 12, 17, 11, 19, 13, 15, 13, 23, 15, 22, 15, 21, 17, 29, 15, 31, 21, 23, 19, 27, 20, 37, 21, 27, 23, 41, 19, 43, 25, 29, 25, 47, 25, 44, 25, 35, 29, 53, 25, 43, 31, 39, 31, 59, 27, 61, 33, 41, 38, 51, 27, 67, 37, 47, 31, 71, 35, 73

Offset: 1

Author

Labos Elemer, Aug 08 2002

Keywords

• nonn
• easy

Comments

Old name was: Number of numbers "related" to n: either divisors or terms in RRS of n.

RRS of n means reduced residue system modulo n. One considers here the smallest positive one. - Wolfdieter Lang, Jan 16 2016

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000005 (tau), A000010 (phi), A045763, A134673.

Programs

Mathematica

DivisorSigma[0, #] + EulerPhi[#] - 1 & /@ Range[73] (* Jayanta Basu, Jul 09 2013 *)

PARI

a(n)=my(f=factor(n)); numdiv(f)+eulerphi(f)-1 \\ Charles R Greathouse IV, Nov 14 2014

Formula

a(n) = n - A045763(n) = A000005(n) + A000010(n) - 1.

If p is prime then a(p) = p.

Row sums of triangle A134673. - Gary W. Adamson, Nov 05 2007

Extensions

Replaced Name with formula. - Wesley Ivan Hurt, Nov 24 2021