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A216482 a(n) is the least value of k such that k*n uses only digits 1 and 2. a(n) = -1 if no such multiple exists.

%I A216482 #13 Dec 27 2022 02:38:30
%S A216482 1,1,4,3,-1,2,3,14,1358,-1,1,1,17,8,-1,7,13,679,59,-1,1,1,527,88,-1,
%T A216482 47,786,4,418,-1,362,66,34,33,-1,617,3,319,2849,-1,271,291,284,48,-1,
%U A216482 2657,26,44,229,-1,22,406,4,393,-1,2,3723,209,19,-1,2,181,194,33,-1,17,33,1634,3219,-1,172,1696,2907,3,-1,1462,1443,1554,28,-1,262,271,134,1443
%N A216482 a(n) is the least value of k such that k*n uses only digits 1 and 2. a(n) = -1 if no such multiple exists.
%H A216482 Robert Israel, <a href="/A216482/b216482.txt">Table of n, a(n) for n = 1..10000</a>
%p A216482 f:= proc(n) local d,a,i,S,R;
%p A216482   if n mod 5 = 0 then return -1 fi;
%p A216482   for d from ilog10(n)+1 do
%p A216482      a:= (10^d-1)/9;
%p A216482      S:= [seq(10^i, i=0..d-1)];
%p A216482      R:= select(t -> convert(t,`+`) + a mod n = 0, combinat:-powerset(S));
%p A216482      if R <> [] then return min(map(t -> convert(t,`+`)+a, R))/n fi
%p A216482   od
%p A216482 end proc:
%p A216482 map(f, [$1..100]); # _Robert Israel_, Dec 26 2022
%Y A216482 Cf. A004290, A079339, A181060, A181061.
%K A216482 sign,base,look
%O A216482 1,3
%A A216482 _V. Raman_, Sep 07 2012