|
|
A097652
|
|
Numbers n such that n=phi(phi(n)+sigma(n)) and n is not of the form 2*p where p is a Sophie Germain odd prime.
|
|
1
|
|
|
1, 2, 20, 48, 180, 208, 864, 1120, 1368, 3552, 58320, 76416, 79968, 95488, 107520, 338688, 570240, 595968, 653184, 1347840, 5199552, 7918848, 14592000, 93699072, 159138176, 167078784, 246688000, 281640960, 314548224, 323985408, 338411520, 347578368, 352002048
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
It is obvious that if n=2*p where p is a Sophie Germain odd prime then n=phi(phi(n)+sigma(n)). This sequence is a subsequence of A097646. Except for the first term all terms of this sequence are even. There is no other term up to 3*10^7.
|
|
LINKS
|
|
|
EXAMPLE
|
14592000 is in the sequence because 14592000=2*7296000, 7296000 is not a Sophie Germain odd prime and phi(phi(14592000)+sigma(14592000)) =14592000.
|
|
MATHEMATICA
|
Do[If[(!PrimeQ[n/2]||!PrimeQ[n+1])&&n==EulerPhi[EulerPhi[n]+ DivisorSigma[1, n]], Print[n]], {n, 30000000}]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|