login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A110173 Least k such that phi(n)=phi(k)+phi(n-k) for 0<k<n, or 0 if there is no k, where phi is Euler's totient function. 3
0, 0, 1, 2, 0, 0, 0, 4, 4, 4, 0, 6, 0, 4, 5, 8, 0, 6, 0, 6, 5, 6, 0, 6, 6, 4, 11, 6, 0, 0, 0, 16, 6, 8, 10, 12, 0, 4, 13, 12, 0, 12, 0, 6, 7, 8, 0, 12, 0, 10, 16, 6, 0, 6, 26, 12, 19, 26, 0, 30, 0, 4, 12, 32, 24, 24, 0, 6, 23, 28, 0, 18, 0, 10, 12, 8, 24, 12, 0, 24, 0, 8, 0, 24, 8, 4, 6, 12, 0, 30 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

Sequence A110174 gives the number of solutions 0<k<n. Note that a(n)=0 for all primes except 3. It is also zero for the composite numbers in A110175.

LINKS

Table of n, a(n) for n=1..90.

MATHEMATICA

a[n_] := Select[Range[n-1], EulerPhi[n]==EulerPhi[n-# ]+EulerPhi[ # ]&]; Table[s=a[n]; If[Length[s]==0, 0, First[s]], {n, 150}]

CROSSREFS

Cf. A066426 (least k such that phi(n)+phi(k)=phi(n+k)).

Sequence in context: A129183 A280292 A181566 * A328820 A259863 A283666

Adjacent sequences:  A110170 A110171 A110172 * A110174 A110175 A110176

KEYWORD

nonn

AUTHOR

T. D. Noe, Jul 15 2005

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 17 22:15 EDT 2021. Contains 343992 sequences. (Running on oeis4.)