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 A258083 Smallest multiple of 3 not appearing earlier that ends with n. 6
 21, 12, 3, 24, 15, 6, 27, 18, 9, 210, 111, 312, 213, 114, 315, 216, 117, 318, 219, 120, 321, 222, 123, 324, 225, 126, 327, 228, 129, 30, 231, 132, 33, 234, 135, 36, 237, 138, 39, 240, 141, 42, 243, 144, 45, 246, 147, 48, 249, 150, 51, 252, 153, 54, 255, 156 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(10*n) = 10*a(n). The sequence is a permutation of the positive multiples of 3. - Vladimir Shevelev, May 24 2015 24 ends with 24 but as 24 is the least element divisible by 3 that ends with 4, it's already used and a(24) = 324. Generally, a(n) = k * 10^d + n with k in {0,1,2,3} and d the number of digits of n. - David A. Corneth, May 24 2015 A258225(n) = a(n) / 3 is a permutation of the positive integers. - Reinhard Zumkeller, May 27 2015 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..9999 Éric Angelini, Multiples of 3 ending with n, SeqFan list, May 23 2015. MATHEMATICA a[n_] := a[n] = For[k=3, True, k=k+3, If[Divisible[k-n, 10^IntegerLength[n] ] && FreeQ[Array[a, n-1], k], Return[k]]]; Array[a, 56] (* Jean-François Alcover, Feb 06 2018 *) PROG (Haskell) import Data.List (isPrefixOf, delete) a258083 n = a258083_list !! (n-1) a258083_list = f 1 \$ tail \$ zip a008585_list \$ map (reverse . show) a008585_list where f x ws = g ws where g ((u, vs) : uvs) = if isPrefixOf xs vs then u : f (x + 1) (delete (u, vs) ws) else g uvs xs = reverse \$ show x (PARI) a(n) = {my(d = digits(n), s = vecsum(d), k); if(s%3 > 0, k = (3 - s%3)%3, i=1; while(i < #d && d[i] == 3, i++); if(i<#d && d[i+1] >= 1 && d[i]-1 == bitand(d[i]-1, 1), k = 3)); k*10^#d + n} \\ David A. Corneth, May 24 2015 CROSSREFS Cf. A008585, A258188, A258217, A258225. Sequence in context: A270790 A300887 A301497 * A260527 A260529 A166033 Adjacent sequences: A258080 A258081 A258082 * A258084 A258085 A258086 KEYWORD nonn,base,look,hear AUTHOR Eric Angelini and Reinhard Zumkeller, May 23 2015 STATUS approved

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Last modified September 30 21:47 EDT 2023. Contains 365801 sequences. (Running on oeis4.)