|
| |
|
|
A070170
|
|
Numbers n such that sigma(n-phi(n))=phi(n).
|
|
1
| |
|
|
2, 15, 39, 255, 627, 939, 1431, 1581, 2409, 3459, 4797, 14289, 20619, 30987, 31935, 43791, 57291, 68991, 71193, 73749, 74841, 94671, 120669, 121227, 132297, 148161, 162843, 196449, 200787, 209451, 217191, 302907, 308937, 434733, 439959, 455961
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| All terms 2 < a(n) < 20000000 are odd and divisible by 3. Most are squarefree.
|
|
|
FORMULA
| From numerical observation if n>31 : ln(n)^10<a(n)<ln(n)^11.
|
|
|
MATHEMATICA
| Do[s=DivisorSigma[1, (n-EulerPhi[n])]-EulerPhi[n]; If[Equal[s, 0], Print[n]], {n, 1, 2000000}]
|
|
|
PROG
| (PARI) for(n=2, 2000000, if(sigma(n-eulerphi(n))==eulerphi(n), print1(n, ", ")))
|
|
|
CROSSREFS
| Cf. A070171.
Sequence in context: A007217 A180223 A070009 * A033568 A200156 A032016
Adjacent sequences: A070167 A070168 A070169 * A070171 A070172 A070173
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| Benoit Cloitre and Elemer Labos, May 06 2002
|
|
|
EXTENSIONS
| Edited by Charles R Greathouse IV (charles.greathouse(AT)case.edu), Oct 28 2009
|
| |
|
|
