The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A074887 Numbers n such that sigma(n - phi(n)) = phi(n + phi(n)). 0

%I #9 Feb 11 2014 19:05:30

%S 915,12957,20745,26985,54621,97785,111615,188013,191775,197631,231045,

%T 258687,428745,565761,726645,793653,807639,829857,941451,1048719,

%U 1084587,1224111,1233027,1863255,1920681,1973805,2043489,2129883,2254119,2265417,2300151

%N Numbers n such that sigma(n - phi(n)) = phi(n + phi(n)).

%e sigma(915-phi(915)) = sigma(915-480) = 720; phi(915+phi(915)) = phi(1395) = 720, so 915 is a term of the sequence.

%t r = {}; Do[e = EulerPhi[n]; If[DivisorSigma[1, n - e] == EulerPhi[n + e], r = Append[r, n]], {n, 1, 10^5}]; r

%t Select[Range[3000000],DivisorSigma[1,#-EulerPhi[#]]==EulerPhi[#+ EulerPhi[ #]]&] (* _Harvey P. Dale_, Sep 03 2013 *)

%K nonn

%O 1,1

%A _Joseph L. Pe_, Sep 13 2002

%E More terms from _Harvey P. Dale_, Sep 03 2013

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 15 20:25 EDT 2024. Contains 375955 sequences. (Running on oeis4.)