OFFSET
1,1
COMMENTS
The sequence consists of all numbers of the form 2p with p prime, along with 8, 12, 18, 24 and 60. See sketch of proof in A066522.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
MATHEMATICA
a = {}; Do[ If[ !PrimeQ[n], k = Select[ Divisors[n], # <= Sqrt[n] &]; If[ Last[k] == Length[k], a = Append[a, n]]], {n, 1, 500} ]; a
dQ[n_]:=!PrimeQ[n]&&Union[Differences[Select[Divisors[n], #<=Sqrt[n]&]]] == {1}; Select[Range[500], dQ] (* Harvey P. Dale, Nov 06 2013 *)
PROG
(Haskell)
a066664 n = a066664_list !! (n-1)
a066664_list = filter ((== 0) . a010051) $ tail a066522_list
-- Reinhard Zumkeller, Nov 14 2011
CROSSREFS
KEYWORD
nice,nonn,easy
AUTHOR
Robert G. Wilson v, Jan 07 2002
STATUS
approved