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

5, 25, 62, 151, 381, 833, 2163, 5291, 13317, 33519, 85179, 213083, 539212, 1344272, 3358571

Offset

1,1

Comments

Inspired by a discussion on the math-fun list on April 18, 2012 by James R. Buddenhagen.

Links

Table of n, a(n) for n=1..15.

Prog

(Haskell)
oddDigits 0 = True
oddDigits n = let (q, r) = quotRem n 10
..............in (odd r) && oddDigits q
oddSet 0 = []
oddSet 1 = [1, 3..9]
oddSet k = [n | i <- [1, 3..9], x <- oddSet (k-1), let n = i*10^(k-1) + x,
...............oddDigits((n^3) `mod` 10^k)]
main = putStrLn $ map (length . oddSet) [1..]

Crossrefs

Cf. A085597 (n such that both n and n^3 have all odd digits).

Sequence in context: A152734 A080856 A060820 * A146404 A323187 A179131

Adjacent sequences: A182208 A182209 A182210 * A182212 A182213 A182214

Keyword

nonn,base

Author

Victor S. Miller, Apr 18 2012

Status

approved