A039649 - OEIS

%I #35 Sep 08 2022 08:44:53

%S 2,2,3,3,5,3,7,5,7,5,11,5,13,7,9,9,17,7,19,9,13,11,23,9,21,13,19,13,

%T 29,9,31,17,21,17,25,13,37,19,25,17,41,13,43,21,25,23,47,17,43,21,33,

%U 25,53,19,41,25,37,29,59,17,61,31,37,33,49,21,67,33,45,25,71,25,73,37,41

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

%C a(p) = p for p prime.

%C Records give A000040. - _Omar E. Pol_, Jul 10 2014

%C Which n are divisible by phi(n)+1? See A085118 for a possible answer and references. - _Peter Munn_, Jun 03 2021

%H Vincenzo Librandi, <a href="/A039649/b039649.txt">Table of n, a(n) for n = 1..10000</a>

%H N. J. A. Sloane, <a href="/A115004/a115004.txt">Families of Essentially Identical Sequences</a>, Mar 24 2021 (Includes this sequence)

%F a(n) = A000010(n) + 1.

%F a(n) <= n for n > 1.

%F G.f.: x/(1 - x) + Sum_{k>=1} mu(k)*x^k/(1 - x^k)^2. - _Ilya Gutkovskiy_, Mar 16 2017

%t Table[EulerPhi[n] + 1, {n, 100}] (* _Vincenzo Librandi_, Aug 13 2013 *)

%o (Magma) [EulerPhi(n)+1: n in [1..100]]; // _Vincenzo Librandi_, Aug 13 2013

%o (Haskell)

%o a039649 = (+ 1) . a000010  -- _Reinhard Zumkeller_, Oct 07 2015

%o (PARI) a(n)=eulerphi(n)+1 \\ _Charles R Greathouse IV_, Mar 04 2017

%Y Cf. A000010, A039650, A039651, A039652, A039653, A039654, A039655, A039656, A085118.

%K nonn,easy

%O 1,1

%A _David W. Wilson_

%E Edited by _Charles R Greathouse IV_, Mar 18 2010.