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 A284891 #20 Feb 16 2025 08:33:43 %S A284891 3,34,345,3456,34567,345678,3456789,345678910,34567891011, %T A284891 3456789101112,345678910111213,34567891011121314,3456789101112131415, %U A284891 345678910111213141516,34567891011121314151617,3456789101112131415161718,345678910111213141516171819 %N A284891 Concatenation of the numbers from 3 to n. %C A284891 The a(3) = 3, a(19) = 345678910111213141516171819 are primes in this sequence (for n < 2800). %H A284891 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ConsecutiveNumberSequences.html">Consecutive Number Sequences</a> %Y A284891 Cf. A089987, A262571. %K A284891 base,nonn,easy %O A284891 3,1 %A A284891 _XU Pingya_, Apr 05 2017