A239870 Noncube perfect powers. [Warning: definition does not match the DATA.]

4, 9, 16, 32, 36, 49, 81, 121, 128, 144, 169, 196, 243, 256, 324, 400, 441, 484, 576, 625, 841, 900, 961, 1024, 1156, 1225, 1296, 1369, 1444, 1521, 1600, 1681, 1849, 1936, 2025, 2048, 2187, 2209, 2304, 2401, 2601, 2704, 2916, 3025, 3125, 3249, 3364, 3600

Offset

1,1

Comments

The NAME suggests that this is an erroneous version of A340585 (which includes 25, for example), but the Haskell implementation indicates that the true definition is more complicated. - R. J. Mathar, Jan 13 2021

Links

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

Formula

A052409(a(n)) mod 3 > 0.

Prog

(Haskell)
import Data.Map (singleton, findMin, deleteMin, insert)
a239870 n = a239870_list !! (n-1)
a239870_list = f 9 (3, 2) (singleton 4 (2, 2)) where
   f zz (bz, ez) m
    | xx < zz = if ex `mod` 3 > 0
      then xx : f zz (bz, ez+1) (insert (bx*xx) (bx, ex+1) $ deleteMin m)
      else      f zz (bz, ez+1) (insert (bx*xx) (bx, ex+1) $ deleteMin m)
    | xx > zz = if ez `mod` 3 > 0
      then zz : f (zz+2*bz+1) (bz+1, 2) (insert (bz*zz) (bz, 3) m)
      else      f (zz+2*bz+1) (bz+1, 2) (insert (bz*zz) (bz, 3) m)
    | otherwise = f (zz+2*bz+1) (bz+1, 2) m
    where (xx, (bx, ex)) = findMin m  --  bx ^ ex == xx

Crossrefs

Cf. A097054, A239728, intersection of A007412 and A001597.

Sequence in context: A326958 A281904 A007679 * A068037 A167188 A295720

Adjacent sequences: A239867 A239868 A239869 * A239871 A239872 A239873

Keyword

nonn,obsc

Author

Reinhard Zumkeller, Mar 28 2014

Status

approved