|
|
A173746
|
|
Numbers k such that tau(tau(k)) = rad(k).
|
|
1
|
|
|
1, 2, 4, 16, 27, 64, 72, 96, 108, 288, 432, 486, 648, 768, 972, 1024, 1536, 1728, 3456, 4096, 5832, 6561, 13122, 17496, 20736, 24576, 27648, 39366, 41472, 65536, 98304, 104976, 110592, 147456, 186624, 256000, 262144, 314928, 400000, 419904, 472392
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
Tau = A000005 is the number of divisors of its argument. rad(n) = A007947(n) is the product of the primes dividing n.
Note that rad() is idempotent: rad(rad(n)) = rad(n). - R. J. Mathar, Nov 07 2011
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
288 is in the sequence because tau(288)= 18, tau(18)=6, rad(288)=6.
|
|
MAPLE
|
numtheory[tau](numtheory[tau](n)) ;
end proc:
for n from 1 to 480000 do
printf("%d, ", n) ;
end if;
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|