|
Search: id:A071780
|
|
|
| A071780 |
|
Smallest k > n such that there are exactly n pairs (x,y) (1 <= x <= y <= k) solutions of the equation: phi(xy)=sigma(x)+sigma(y). |
|
+0
1
|
|
| 1, 7, 12, 15, 21, 26, 30, 33, 38, 60, 63, 65, 120, 189, 240, 296, 344, 442, 480, 567, 960, 1476, 1701, 1920
(list; graph; listen)
|
|
|
OFFSET
|
0,2
|
|
|
PROGRAM
|
(PARI) for(n=1, 12, s=2; while(sum(i=1, s, sum(j=1, i, if(eulerphi(i*j)-sigma(i)-sigma(j), 0, 1)))<n, s++); print1(s, ", "))
|
|
CROSSREFS
|
Adjacent sequences: A071777 A071778 A071779 this_sequence A071781 A071782 A071783
Sequence in context: A073255 A072834 A138615 this_sequence A063303 A091215 A090067
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Benoit Cloitre (benoit7848c(AT)orange.fr), Jun 04 2002
|
|
EXTENSIONS
|
More terms from Ryan Propper (rpropper(AT)stanford.edu), Sep 28 2005
|
|
|
Search completed in 0.002 seconds
|
