|
| |
|
|
A071008
|
|
Numbers n such that uphi(uphi(n))=n/2.
|
|
0
| |
|
|
2, 4, 16, 256, 364, 1456, 3276, 13104, 21600, 23296, 65536, 209664, 249984, 367200, 1285632, 3110400, 5963776, 6596304, 9749376, 23046144
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| If n=Product p_i^r_i then uphi(n)=Product ( p_i^r_i-1); for example uphi(12)=(4-1)*(3-1)=6
If 2^n+1 is a Fermat prime then 2^(2*n) is a solution of the equation.
3110400 and 4294967296 are also in the sequence.
|
|
|
FORMULA
| {n: 2*A047994(A047994(n)) = n}.
|
|
|
PROG
| (PARI) forstep(n=2, 1e9, 2, A047994(A047994(n))*2-n|print1(n", ")) \\ - M. F. Hasler, Nov 20 2010
|
|
|
CROSSREFS
| Cf. A030163.
Sequence in context: A050472 A109457 A105788 * A178077 A001146 A114641
Adjacent sequences: A071005 A071006 A071007 * A071009 A071010 A071011
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Yasutoshi Kohmoto (zbi74583(AT)boat.zero.ad.jp)
|
|
|
EXTENSIONS
| More terms from R. J. Mathar, A. P. Heinz and M. F. Hasler, Nov 20 2010
|
| |
|
|
