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 A223475 Least k such that the decimal representation of k*n has digits in nonincreasing order. 2
 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 4, 3, 2, 2, 3, 3, 4, 1, 1, 1, 4, 3, 2, 2, 2, 3, 3, 1, 1, 1, 1, 13, 2, 2, 2, 2, 17, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 15, 13, 9, 9, 1, 1, 1, 1, 1, 1, 1, 13, 8, 8, 1, 1, 1, 1, 1, 1, 1, 1, 84, 7, 1, 1, 1, 1, 1, 1, 1, 1, 1, 86, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 11, 5, 7, 5, 2, 5, 3, 4, 6, 1, 1, 75, 47, 38, 8, 45, 56, 8, 7, 5, 55, 5, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 LINKS Giovanni Resta, Table of n, a(n) for n = 1..2000 EXAMPLE 39*17 = 663 has digits in nonincreasing order, and no k < 17 has this property, hence a(39) = 17. MATHEMATICA a[n_] := a[nn_] := Block[{n = nn, f, w = Range@9, k = 1}, While[Mod[n, 10] == 0, n /= 10]; While[(f = Select[w, Max@ Differences@ IntegerDigits[n*#] <= 0 &, 1]) == {}, k++; w = Union@ Flatten@Table[ Select[d*10^(k-1) + w, Max@ Differences@ IntegerDigits[Mod[n*#, 10^k], 10, k] <= 0 &], {d, 0, 9}]]; f[[1]]]; Array[a, 123] (* faster than basic approach. Giovanni Resta, Mar 26 2013 *) CROSSREFS a(n)*n yields sequence A223474. Cf. A079339, A181061. Cf. A009996. Sequence in context: A276373 A317173 A190302 * A190137 A003561 A201327 Adjacent sequences: A223472 A223473 A223474 * A223476 A223477 A223478 KEYWORD nonn,base AUTHOR Paul Tek, Mar 20 2013 STATUS approved

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Last modified November 28 17:03 EST 2023. Contains 367419 sequences. (Running on oeis4.)