|
| |
|
|
A141113
|
|
Positive integers n such that d(d(n)) divides n, where d(n) is the number of divisors of n.
|
|
3
| |
|
|
1, 2, 4, 6, 12, 15, 16, 20, 21, 24, 27, 28, 32, 33, 36, 39, 40, 44, 48, 51, 52, 56, 57, 60, 64, 68, 69, 72, 76, 80, 84, 87, 88, 90, 92, 93, 96, 104, 108, 111, 112, 116, 120, 123, 124, 126, 128, 129, 132, 136, 141, 144, 148, 150, 152, 156, 159, 164, 172, 176, 177, 180
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,2
|
|
|
EXAMPLE
| 28 has 6 divisors and 6 has 4 divisors. 4 divides 28, so 28 is in the sequence.
|
|
|
MAPLE
| with(numtheory): a:=proc(n) if `mod`(n, tau(tau(n))) = 0 then n else end if end proc: seq(a(n), n=1..200); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 05 2008
|
|
|
MATHEMATICA
| Select[Range[200], Divisible[#, DivisorSigma[0, DivisorSigma[0, #]]]&] (* From Harvey P. Dale, Feb 05 2012 *)
|
|
|
CROSSREFS
| Cf. A010553, A141114, A141115.
Sequence in context: A015663 A057830 A013916 * A050584 A019280 A090748
Adjacent sequences: A141110 A141111 A141112 * A141114 A141115 A141116
|
|
|
KEYWORD
| nonn,changed
|
|
|
AUTHOR
| Leroy Quet Jun 04 2008
|
|
|
EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 05 2008
|
| |
|
|
