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A258188 Smallest multiple of 7 not appearing earlier that ends with n.

%I A258188 #20 Feb 07 2018 12:14:37
%S A258188 21,42,63,14,35,56,7,28,49,210,511,112,413,714,315,616,217,518,119,
%T A258188 420,721,322,623,224,525,126,427,728,329,630,231,532,133,434,735,336,
%U A258188 637,238,539,140,441,742,343,644,245,546,147,448,749,350,651,252,553,154
%N A258188 Smallest multiple of 7 not appearing earlier that ends with n.
%C A258188 a(10*n) = 10*a(n).
%C A258188 The sequence is a permutation of the positive multiples of 7. - _Vladimir Shevelev_, May 24 2015
%C A258188 A258329(n) = a(n) / 7 is a permutation of the positive integers. - _Reinhard Zumkeller_, May 27 2015
%H A258188 Reinhard Zumkeller, <a href="/A258188/b258188.txt">Table of n, a(n) for n = 1..9999</a>
%t A258188 a[n_] := a[n] = For[k = 7, True, k = k + 7, If[Divisible[k - n, 10^IntegerLength[n]] && FreeQ[Array[a, n-1], k], Return[k]]]; Array[a, 54] (* _Jean-François Alcover_, Feb 07 2018 *)
%o A258188 (Haskell)
%o A258188 import Data.List (isPrefixOf, delete)
%o A258188 a258188 n = a258188_list !! (n-1)
%o A258188 a258188_list = f 1 $ tail $ zip
%o A258188    a008589_list $ map (reverse . show) a008589_list where
%o A258188    f x ws = g ws where
%o A258188      g ((u, vs) : uvs) = if isPrefixOf xs vs
%o A258188                          then u : f (x + 1) (delete (u, vs) ws) else g uvs
%o A258188      xs = reverse $ show x
%Y A258188 Cf. A008589, A258083, A258217, A258329.
%K A258188 nonn,base
%O A258188 1,1
%A A258188 _Eric Angelini_ and _Reinhard Zumkeller_, May 23 2015