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 A309706 #35 Dec 08 2019 02:09:38 %S A309706 2,23,235,2357,112357,112357,112357,1123579,1123579,1123579,1231579, %T A309706 1231579,12341579,12431579,12431579,12453179,12453179,124536179, %U A309706 124536179,1124536719,1234567139,1234567139,12345671839,12345671839,12456783197,102456783197,102456783197,102456783197 %N A309706 Smallest number that contains the first n primes as substrings in base 10. Substrings go from left to right, but numbers in the substrings can be separated by several numbers. %C A309706 The version with subsequences of contiguous numbers is A054261. %C A309706 The sequence is nondecreasing, by definition. %F A309706 a(n) <= A054261(n). - _David A. Corneth_, Aug 28 2019 %e A309706 The series starts as A054261, but 112357 is followed by 112357 because 13 can be obtained with a subsequence '1','3' which is interrupted by '2'. %Y A309706 Cf. A054261, A240959. %K A309706 nonn,base %O A309706 1,1 %A A309706 _Vincent Champain_, Aug 28 2019 %E A309706 a(11)-a(28) from _David A. Corneth_, Aug 28 2019