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Numbers k such that every base-7 digit of k is a base-9 digit of k.
4

%I #15 Aug 05 2021 07:02:09

%S 1,2,3,4,5,6,31,99,106,107,195,198,248,257,284,297,321,498,514,749,

%T 750,751,758,767,785,936,939,940,943,950,968,996,1028,1086,1088,1110,

%U 1163,1200,1218,1254,1453,1471,1498,1500,1502,1507

%N Numbers k such that every base-7 digit of k is a base-9 digit of k.

%H Reinhard Zumkeller, <a href="/A037403/b037403.txt">Table of n, a(n) for n = 1..10000</a>

%o (Haskell)

%o import Data.List ((\\), nub)

%o a037403 n = a037403_list !! (n-1)

%o a037403_list = filter f [1..] where

%o f x = null $ nub (ds 7 x) \\ nub (ds 9 x)

%o ds b x = if x > 0 then d : ds b x' else [] where (x', d) = divMod x b

%o -- _Reinhard Zumkeller_, May 30 2013

%Y Cf. A007093, A007095.

%Y Cf. A037402, A037404.

%K nonn,base

%O 1,2

%A _Clark Kimberling_