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A337707
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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.
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1
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11, 121, 99, 1898, 12898, 123898, 1234898, 12345898, 123456898, 110, 1909, 10330, 9188, 9088, 19787, 129787, 1239787, 12349787, 123459787, 1210, 12909, 103430, 1024540, 2988, 1988, 27987, 237987, 2347987, 23457987, 12310, 123909, 1034530, 10245640, 102356750, 988, 12988
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OFFSET
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1,1
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COMMENTS
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Does the term -1 first appear at a(55)?
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LINKS
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EXAMPLE
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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).
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PROG
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(PARI) isokd(n) = my(d=digits(n)); #d != #Set(d); \\ A109303
isok(k, n) = {if (! isokd(k-1), for (i=k, k+n-1, if (! isokd(i), return (0)); ); ! isokd(k+n); ); }
a(n) = {my(k=1); while (!isok(k, n), k++); k; } \\ Michel Marcus, Jan 13 2022
(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
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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