This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181073 #20 Jul 28 2019 21:48:07 %S A181073 1,1243,1423,2143,2341,2413,2431,3241,3421,4123,4213,4231,4321, %T A181073 1234567,1234657,1235467,1235647,1236457,1236547,1243567,1243657, %U A181073 1245367,1245637,1245673,1245763,1246357,1246537,1246573,1246753 %N A181073 Permutations of lengths 1,2,3,... arranged lexicographically that are relatively prime to 30. %C A181073 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. %C A181073 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). %H A181073 Marco Ripà, <a href="http://www.rudimatematici.com/Bookshelf/divisibilitaper3.pdf"> Divisibilità per 3 degli elementi di particolari sequenze numeriche</a> %H A181073 Marco Ripà, <a href="http://www.scribd.com/doc/47337392/On-prime-factors-in-old-and-new-sequences-of-integers">On prime factors in old and new sequences of integers</a> %t A181073 f[n_] := Select[ FromDigits@ # & /@ Permutations@ Range@ n, Mod[#, 2] != 0 && Mod[#, 3] != 0 && Mod[#, 5] != 0 &]; Take[ Flatten@ Array[f, 7], 35] %Y A181073 Cf. A030299, A030298. %K A181073 nonn,easy,base,less %O A181073 1,2 %A A181073 _Marco Ripà_, Jan 23 2011