OFFSET
1,2
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = (10*13)/((10-1)*(13-1)) = 65/54. - Amiram Eldar, Sep 25 2020
a(n) ~ exp(sqrt(2*log(10)*log(13)*n)) / sqrt(130). - Vaclav Kotesovec, Sep 25 2020
MATHEMATICA
n = 10^7; Flatten[Table[10^i*13^j, {i, 0, Log10[n]}, {j, 0, Log[13, n/10^i]}]] // Sort (* Amiram Eldar, Sep 25 2020 *)
PROG
(Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a108761 n = a108761_list !! (n-1)
a108761_list = f $ singleton (1, 0, 0) where
f s = y : f (insert (10 * y, i + 1, j) $ insert (13 * y, i, j + 1) s')
where ((y, i, j), s') = deleteFindMin s
-- Reinhard Zumkeller, May 15 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Douglas Winston (douglas.winston(AT)srupc.com), Jun 24 2005
STATUS
approved