OFFSET
1,2
COMMENTS
A072965(a(n)) = 1.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
EXAMPLE
a(99)=1040399=1019*1021; a(101)=1090125=(3*5)*(3*5)*(3*5)*(17*19); a(103)=1101275=(5*7)*(5*7)*(29*31); a(105)=1126125= (3*5)*(3*5)*(5*7)*(11*13).
MATHEMATICA
max = 70000; t1 = Select[Prime /@ Range[PrimePi[Sqrt[max]]], PrimeQ[# + 2] &]; pairs = Join[{1}, t1*(t1 + 2)]; f[pairs_] := Outer[Times, pairs, pairs] // Flatten // Union // Select[#, # <= max &] &; FixedPoint[f, pairs] (* Jean-François Alcover, Dec 11 2012 *)
PROG
(Haskell)
import Data.Set (Set, singleton, delete, findMin, deleteFindMin, insert)
a074480 n = a074480_list !! (n-1)
a074480_list = multClosure a037074_list where
multClosure [] = [1]
multClosure (b:bs) = 1:h [b] (singleton b) bs where
h cs s [] = m:h (m:cs) (foldl (flip insert) s' $ map (*m) cs) []
where (m, s') = deleteFindMin s
h cs s xs'@(x:xs)
| m < x = m:h (m:cs) (foldl (flip insert) s' $ map (*m) cs) xs'
| otherwise = x:h (x:cs) (foldl (flip insert) s $ map (*x) (x:cs)) xs
where (m, s') = deleteFindMin s
-- Reinhard Zumkeller, Aug 14 2011
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
Reinhard Zumkeller, Aug 23 2002
STATUS
approved