cp's OEIS Frontend

A182211 The number of integers k < 10^n such that both k and k^3 mod 10^n have all odd decimal digits.

%I A182211 #17 Dec 09 2017 19:12:06
%S A182211 5,25,62,151,381,833,2163,5291,13317,33519,85179,213083,539212,
%T A182211 1344272,3358571
%N A182211 The number of integers k < 10^n such that both k and k^3 mod 10^n have all odd decimal digits.
%C A182211 Inspired by a discussion on the math-fun list on April 18, 2012 by _James R. Buddenhagen_.
%o A182211 (Haskell)
%o A182211 oddDigits 0 = True
%o A182211 oddDigits n = let (q,r) = quotRem n 10
%o A182211 ..............in (odd r) && oddDigits q
%o A182211 oddSet 0 = []
%o A182211 oddSet 1 = [1,3..9]
%o A182211 oddSet k = [n | i <- [1,3..9], x <- oddSet (k-1), let n = i*10^(k-1) + x,
%o A182211 ...............oddDigits((n^3) `mod` 10^k)]
%o A182211 main = putStrLn $ map (length . oddSet) [1..]
%Y A182211 Cf. A085597 (n such that both n and n^3 have all odd digits).
%K A182211 nonn,base
%O A182211 1,1
%A A182211 _Victor S. Miller_, Apr 18 2012