login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A239870 Noncube perfect powers. 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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

AUTHOR

Reinhard Zumkeller, Mar 28 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 1 13:18 EDT 2020. Contains 333159 sequences. (Running on oeis4.)