OFFSET
1,2
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = 5/4. - Amiram Eldar, Mar 29 2025
MATHEMATICA
With[{max = 10^7}, Flatten[Table[9^i*10^j, {i, 0, Log[9, max]}, {j, 0, Log[10, max/9^i]}]] // Sort] (* Amiram Eldar, Mar 29 2025 *)
PROG
(Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a025635 n = a025635_list !! (n-1)
a025635_list = f $ singleton (1, 0, 0) where
f s = y : f (insert (9 * y, i + 1, j) $ insert (10 * y, i, j + 1) s')
where ((y, i, j), s') = deleteFindMin s
-- Reinhard Zumkeller, May 15 2015
(PARI) list(lim)=my(v=List(), N); for(n=0, logint(lim\=1, 10), N=10^n; while(N<=lim, listput(v, N); N*=9)); Set(v) \\ Charles R Greathouse IV, Jan 10 2018
(Python)
from sympy import integer_log
def A025635(n):
def bisection(f, kmin=0, kmax=1):
while f(kmax) > kmax: kmax <<= 1
kmin = kmax >> 1
while kmax-kmin > 1:
kmid = kmax+kmin>>1
if f(kmid) <= kmid:
kmax = kmid
else:
kmin = kmid
return kmax
def f(x): return n+x-sum(integer_log(x//10**i, 9)[0]+1 for i in range(integer_log(x, 10)[0]+1))
return bisection(f, n, n) # Chai Wah Wu, Mar 25 2025
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
STATUS
approved