A122494 Numbers of the form a^b with 2<=a<=b.

4, 8, 16, 27, 32, 64, 81, 128, 243, 256, 512, 729, 1024, 2048, 2187, 3125, 4096, 6561, 8192, 15625, 16384, 19683, 32768, 46656, 59049, 65536, 78125, 131072, 177147, 262144, 279936, 390625, 524288, 531441, 823543, 1048576, 1594323, 1679616

Offset: 1

Author

Paul Stoeber (pstoeber(AT)uni-potsdam.de), Sep 16 2006

Keywords

• nonn

Examples

			279936 is there because it is 6^7.
		

Links

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

Crossrefs

Subsequences: A000312, A257278.

Programs

Haskell

import Data.Set (singleton, deleteFindMin, insert)
a122494 n = a122494_list !! (n-1)
a122494_list = f (singleton (4, 2)) 27 [3..] where
   f s uu us@(u:us'@(u':_))
     | vv > uu = uu : f (insert (uu * u, u) s) (u' ^ u') us'
     | vv < uu = vv : f (insert (vv * v, v) s') uu us
     | otherwise = vv : f (insert (vv * v, v) s') (u' ^ u') us'
     where ((vv, v), s') = deleteFindMin s
-- Reinhard Zumkeller, May 01 2015