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A182272 Starting with 1, smallest integer not yet in the sequence such that two neighboring digits in the sequence multiply to a composite.

%I A182272 #16 Feb 05 2025 22:11:22
%S A182272 1,4,2,3,5,6,7,8,9,10,14,16,18,19,20,22,23,24,25,26,27,28,29,30,32,33,
%T A182272 34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,52,53,54,55,56,57,
%U A182272 58,59,60,61,62,63,64,65,66,67,68,69,70,72,73,74,75,76
%N A182272 Starting with 1, smallest integer not yet in the sequence such that two neighboring digits in the sequence multiply to a composite.
%C A182272 For this sequence, 0 is considered composite.
%H A182272 Dominic McCarty, <a href="/A182272/b182272.txt">Table of n, a(n) for n = 1..10000</a>
%o A182272 (Python)
%o A182272 a, z = [1], [1, 2, 3, 5, 7]
%o A182272 while len(a) < 100:
%o A182272     k, s = 2, "2"
%o A182272     while (k in a) or (a[-1] % 10 * int(s[0]) in z) or \
%o A182272         any(int(s[n]) * int(s[n+1]) in z for n in range(0, len(s)-1)): s, k = str(k+1), k+1
%o A182272     a.append(k)
%o A182272 print(a) # _Dominic McCarty_, Feb 05 2025
%K A182272 nonn,base
%O A182272 1,2
%A A182272 _Jim Nastos_ and _Eric Angelini_, Apr 22 2012