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 A307177 #19 Mar 29 2019 13:07:51
%S A307177 1,0,1,2,0,1,4,0,1,5,2,1,6,2,4,2,5,3,0,3,2,7,2,8,1,8,3,5,4,5,6,3,6,4,
%T A307177 8,4,9
%N A307177 Decimal expansion of smallest nontrivial base-10 number that contains all pairwise products of its digits as substrings.
%C A307177 "Pairwise products" includes the squares of the digits.
%C A307177 Suggested by Ricardo Palomino, who mentioned the trivial numbers A007088.
%C A307177 If any digit other than 0 or 1 appears, then all ten digits appear, as can easily be checked for each digit. For example, if 2 appears then 2*2 = 4 appears, which implies that 2*4 = 8 appears and {1,6} (from 4*4 = 16) appear, which implies that 3 appears (from 4*8 = 32), which implies that 3*3 = 9 appears, which implies that {2,7} appear (from 3*9), which implies that {5,6} appear (from 7*8), which implies that 0 appears (from 2*5 = 10).
%C A307177 There are 37 distinct products (10 with one digit and 27 with two digits) of pairs of digits from {0,1,...,9}.
%C A307177 Rob Pratt solved an asymmetric traveling salesman problem (ATSP) on 38 nodes to find the minimum number of digits, which turns out to be 37, and then solved a sequence of integer linear programming problems (minimizing one digit at a time from left to right) to find the minimum such 37-digit number.
%e A307177 1012014015216242530327281835456364849.
%Y A307177 A203565 considers only products of adjacent digits.
%K A307177 nonn,cons,fini,full,base
%O A307177 37,4
%A A307177 _Rob Pratt_, Mar 27 2019