OFFSET
1,2
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Repunit
Wikipedia, Repunit
EXAMPLE
a(13)=1234321=1111^2; a(14)=1367631=111^3; a(15)=1771561=11^6.
MATHEMATICA
With[{intlen=12}, Select[Union[Flatten[#^Range[intlen]&/@(FromDigits/@ Table[ PadRight[{}, n, 1], {n, intlen}])]], IntegerLength[#]<=intlen&]] (* Harvey P. Dale, Apr 25 2016 *)
PROG
(Haskell)
import Data.Set (empty, findMin, deleteMin, deleteMin, insert)
import qualified Data.Set as Set (null)
a083278 n = a083278_list !! (n-1)
a083278_list = 1 : f empty (drop 2 a002275_list) where
f rups rus'@(ru:rus)
| Set.null rups || m > ru = f (insert (ru, ru) rups) rus
| otherwise = m : f (insert (m*m', m') (deleteMin rups)) rus'
where (m, m') = findMin rups
-- Reinhard Zumkeller, Feb 05 2012
(PARI) lista(nn) = {my(list = List(), r); for (n=1, nn, my(r = (10^n-1)/9); listput(list, r); if (r > 1, my(e=2); while(#Str(x=r^e) <= nn, listput(list, x); e++)); ); Vec(vecsort(list)); } \\ Michel Marcus, May 28 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, Jun 02 2003
STATUS
approved