cp's OEIS Frontend

A337707 a(n) is the lowest number in the sequence of the first occurrence of exactly n consecutive numbers with at least one repeated digit, or -1 if no such number exists.

%I A337707 #54 Jan 17 2022 10:08:55
%S A337707 11,121,99,1898,12898,123898,1234898,12345898,123456898,110,1909,
%T A337707 10330,9188,9088,19787,129787,1239787,12349787,123459787,1210,12909,
%U A337707 103430,1024540,2988,1988,27987,237987,2347987,23457987,12310,123909,1034530,10245640,102356750,988,12988
%N A337707 a(n) is the lowest number in the sequence of the first occurrence of exactly n consecutive numbers with at least one repeated digit, or -1 if no such number exists.
%C A337707 Terms computed by _Claudio Meller_.
%C A337707 Does the term -1 first appear at a(55)?
%C A337707 All terms < 9876543210. - _Robert Israel_, Jan 14 2022
%H A337707 Michel Marcus, <a href="/A337707/b337707.txt">Table of n, a(n) for n = 1..54</a>
%H A337707 Michel Marcus, <a href="/A337707/a337707.txt">Positions and lengths</a>
%H A337707 Michel Marcus, <a href="/A337707/a337707_1.txt">Lengths and positions</a>
%e A337707 a(3) = 99 is the smallest number in the first appearance sequence of 3 consecutive numbers with repeated digits, 99, 100 and 101, a(15) = 19787 is the smallest number in the first appearance sequence of 15 consecutive numbers with repeated digits that starts in 19787 and finish in 19801 (19802 has no repeated digits).
%o A337707 (PARI) isokd(n) = my(d=digits(n)); #d != #Set(d); \\ A109303
%o A337707 isok(k, n) = {if (! isokd(k-1), for (i=k, k+n-1, if (! isokd(i), return (0)););! isokd(k+n););}
%o A337707 a(n) = {my(k=1); while (!isok(k, n), k++); k;} \\ _Michel Marcus_, Jan 13 2022
%o A337707 (PARI) lista(nn) = {my(map=Map(), r=isokd(1), nb, k, nbmax=0); for (n=2, nn, my(rr = isokd(n)); if (r, if (rr, nb++, if (! mapisdefined(map, nb), mapput(map, nb, k)); nb=0),  if (rr, nb=1; k=n, nb=0); ); r = rr; ); map;} \\ _Michel Marcus_, Jan 14 2022
%Y A337707 Cf. A109303.
%K A337707 base,nonn
%O A337707 1,1
%A A337707 _Rodolfo Kurchan_, Sep 26 2020