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 A181073 Permutations of lengths 1,2,3,... arranged lexicographically that are relatively prime to 30. 3
 1, 1243, 1423, 2143, 2341, 2413, 2431, 3241, 3421, 4123, 4213, 4231, 4321, 1234567, 1234657, 1235467, 1235647, 1236457, 1236547, 1243567, 1243657, 1245367, 1245637, 1245673, 1245763, 1246357, 1246537, 1246573, 1246753 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers whose digits are permutations of (1,2,3,4,...,n) for some n >= 1, for which the first 3 primes (2,3,5) do not appear in their factorization. This constitutes the smallest subset of A030299 for which it's possible to synthesize a compact formula to express the generic term: it contains every prime number already in A030299. In fact it corresponds to the subset of the terms of A030299 constructed from the concatenation of k:=1+3*i (for i >= 0) elements belonging to (1,2,3,4,...,n) that are congruent in modulo 10 to (1,3,7,9). LINKS Table of n, a(n) for n=1..29. Marco Ripà, Divisibilità per 3 degli elementi di particolari sequenze numeriche Marco Ripà, On prime factors in old and new sequences of integers MATHEMATICA f[n_] := Select[ FromDigits@ # & /@ Permutations@ Range@ n, Mod[#, 2] != 0 && Mod[#, 3] != 0 && Mod[#, 5] != 0 &]; Take[ Flatten@ Array[f, 7], 35] CROSSREFS Cf. A030299, A030298. Sequence in context: A209711 A228964 A047628 * A023065 A190413 A252675 Adjacent sequences: A181070 A181071 A181072 * A181074 A181075 A181076 KEYWORD nonn,easy,base,less AUTHOR Marco Ripà, Jan 23 2011 STATUS approved

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Last modified August 4 13:44 EDT 2024. Contains 374923 sequences. (Running on oeis4.)