A073757 - OEIS

%I #33 Nov 25 2021 12:43:10

%S 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,

%T 17,29,15,31,21,23,19,27,20,37,21,27,23,41,19,43,25,29,25,47,25,44,25,

%U 35,29,53,25,43,31,39,31,59,27,61,33,41,38,51,27,67,37,47,31,71,35,73

%N a(n) = d(n) + phi(n) - 1.

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

%C RRS of n means reduced residue system modulo n. One considers here the smallest positive one. - _Wolfdieter Lang_, Jan 16 2016

%H Antti Karttunen, <a href="/A073757/b073757.txt">Table of n, a(n) for n = 1..10000</a>

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

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

%F Row sums of triangle A134673. - _Gary W. Adamson_, Nov 05 2007

%t DivisorSigma[0, #] + EulerPhi[#] - 1 & /@ Range[73] (* _Jayanta Basu_, Jul 09 2013 *)

%o (PARI) a(n)=my(f=factor(n)); numdiv(f)+eulerphi(f)-1 \\ _Charles R Greathouse IV_, Nov 14 2014

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

%K nonn,easy

%O 1,2

%A _Labos Elemer_, Aug 08 2002

%E Replaced Name with formula. - _Wesley Ivan Hurt_, Nov 24 2021