A037389 Every base 4 digit of k is a base 7 digit of k.

1, 2, 3, 9, 52, 84, 85, 86, 87, 105, 106, 170, 191, 255, 345, 352, 357, 358, 360, 361, 362, 366, 368, 369, 381, 394, 406, 409, 410, 415, 422, 444, 462, 479, 486, 492, 496, 497, 501, 503, 504, 505, 506, 507, 509, 510, 511, 553, 597

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A037387, A037388, A037390, A037391, A037392.

Programs

Haskell

import Data.List ((\\), nub)
a037389 n = a037389_list !! (n-1)
a037389_list = filter f [1..] where
   f x = null $ nub (ds 4 x) \\ nub (ds 7 x)
   ds b x = if x > 0 then d : ds b x' else []  where (x', d) = divMod x b
-- Reinhard Zumkeller, May 30 2013

Mathematica

Select[Range[600],Complement[IntegerDigits[#,4],IntegerDigits[#,7]]=={}&] (* Harvey P. Dale, Jan 25 2024 *)