OFFSET
1,1
COMMENTS
Numbers k such that phi(k) = (3/7)*k - Benoit Cloitre, Apr 19 2002
Subsequence of A143204. - Reinhard Zumkeller, Sep 13 2011
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
A143201(a(n)) = 6. - Reinhard Zumkeller, Sep 13 2011
Sum_{n>=1} 1/a(n) = 1/6. - Amiram Eldar, Dec 22 2020
MATHEMATICA
With[{nn=20}, Select[Union[Flatten[Table[2^n 7^k, {n, nn}, {k, nn}]]], #<=2^nn 7&]] (* Harvey P. Dale, Nov 25 2020 *)
PROG
(Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a033847 n = a033847_list !! (n-1)
a033847_list = f (singleton (2*7)) where
f s = m : f (insert (2*m) $ insert (7*m) s') where
(m, s') = deleteFindMin s
-- Reinhard Zumkeller, Sep 13 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset fixed by Reinhard Zumkeller, Sep 13 2011
STATUS
approved