A108218 Numbers of the form (11^i)*(12^j), with i, j >= 0.

1, 11, 12, 121, 132, 144, 1331, 1452, 1584, 1728, 14641, 15972, 17424, 19008, 20736, 161051, 175692, 191664, 209088, 228096, 248832, 1771561, 1932612, 2108304, 2299968, 2509056, 2737152, 2985984, 19487171, 21258732, 23191344, 25299648

Offset: 1

Author

Douglas Winston (douglas.winston(AT)srupc.com), Jun 28 2005

Keywords

• nonn
• easy

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003596, A003597, A107988, A003598, A108201, A108698, A064476, A003599, A108238, A107788, A108687, A108779, A108090, A108771.

Programs

Haskell

import Data.Set (singleton, deleteFindMin, insert)
a108218 n = a108218_list !! (n-1)
a108218_list = f $ singleton (1,0,0) where
   f s = y : f (insert (11 * y, i + 1, j) $ insert (12 * y, i, j + 1) s')
         where ((y, i, j), s') = deleteFindMin s
-- Reinhard Zumkeller, May 15 2015

Mathematica

With[{max = 3*10^7}, Flatten[Table[11^i*12^j, {i, 0, Log[11, max]}, {j, 0, Log[12, max/11^i]}]] // Sort] (* Amiram Eldar, Mar 29 2025 *)

Formula

Sum_{n>=1} 1/a(n) = 6/5. - Amiram Eldar, Mar 29 2025