A122494 Set of numbers of the form a^b with 2<=a<=b (rare powers?), sorted.

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

1,1

Links

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

Example

279936 is there because it is 6^7.

Prog

(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

Crossrefs

Subsequences: A000312, A257278.

Sequence in context: A325127 A054744 A100391 * A257278 A257279 A334151

Adjacent sequences: A122491 A122492 A122493 * A122495 A122496 A122497

Keyword

nonn

Author

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

Status

approved