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A182211 The number of integers k < 10^n such that both k and k^3 mod 10^n have all odd decimal digits. 0
5, 25, 62, 151, 381, 833, 2163, 5291, 13317, 33519, 85179, 213083, 539212, 1344272, 3358571 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 18 02:12 EST 2019. Contains 320237 sequences. (Running on oeis4.)