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 A182271 #21 Jun 14 2025 16:15:26 %S A182271 1,2,12,13,15,17,121,3,131,5,151,7,171,21,31,51,71,212,1212,1213,1215, %T A182271 1217,1312,1313,1315,1317,1512,1513,1515,1517,1712,1713,1715,1717, %U A182271 12121,213,12131,215,12151,217,12171,312,13121,313,13131,315,13151,317,13171 %N A182271 Starting with 1, smallest integer not yet in the sequence such that two neighboring digits of the sequence multiply to a prime. %H A182271 Dominic McCarty, <a href="/A182271/b182271.txt">Table of n, a(n) for n = 1..10000</a> %o A182271 (Python) %o A182271 a = [] %o A182271 while len(a) < 49: %o A182271 a.append(1) %o A182271 while (s := "".join(map(str,a))) and a[-1] in a[:-1] or any(s[i] != "1" for i in range(0,len(s),2)) or any(int(s[i]) not in [2,3,5,7] for i in range(1,len(s),2)): a[-1] += 1 %o A182271 print(a) # _Dominic McCarty_, Jun 14 2025 %K A182271 nonn,base %O A182271 1,2 %A A182271 _Eric Angelini_ and _Jim Nastos_, Apr 22 2012