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 A299980 #4 Feb 23 2018 09:48:49
%S A299980 1,10,2,5,4,15,6,17,12,9,20,3,30,7,29,14,22,23,35,8,13,16,19,11,28,18,
%T A299980 25,24,21,40,26,27,38,37,46,44,32,33,31,34,45,36,39,50,41,49,42,43,47,
%U A299980 60,48,55,51,53,57,54,52,58,65,56,59,68,70,61,64,63,62,66,75,67,76,79,71,80,69,73,74,82,72,84,81,87,90,77,78,85,83,88,91
%N A299980 Lexicographic first sequence of positive integers such that a(n)*a(n+1) has a digit 0, and no term occurs twice.
%C A299980 A permutation of the positive integers.
%e A299980 a(1) = 1 is the least positive integer, and a(1) has no other constraint to satisfy.
%e A299980 a(2) = 10 is the least positive integer > a(1) = 1 such that a(2)*a(1) = 10 has a digit 0.
%e A299980 a(3) = 2 is the smallest available positive integer, and such that a(3)*a(2) (= 20) has a digit 0.
%e A299980 a(4) = 5 is the least positive integer not in {1, 2, 10} such that a(4)*a(3) (= 10) has a digit 0: The smaller choices 2, 3 and 4 do not satisfy this.
%o A299980 (PARI) A299980(n,f=1,d=0,a=1,u=[a])={for(n=2,n,f&&if(f==1,print1(a","),write(f,n-1," "a)); for(k=u[1]+1,oo, setsearch(u,k)&&next;setsearch(Set(digits(a*k)),d)&&(a=k)&&break);u=setunion(u,[a]);while(#u>1&&u[2]==u[1]+1,u=u[^1]));a}
%Y A299980 Cf. A299981, A299402, A299403, A298974, A298975, A299996, A299997, A298978, A298979: analog with digit 1, ..., 9.
%Y A299980 Cf. A299957, A299969, ..., A299988: analog with addition instead of multiplication, and different digits.
%K A299980 nonn,base
%O A299980 1,2
%A A299980 _M. F. Hasler_, Feb 22 2018