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 A351998 #9 Mar 13 2022 19:25:09 %S A351998 1,10,12,14,16,18,20,2,3,22,4,5,24,6,7,26,8,9,28,11,30,32,34,36,38,40, %T A351998 13,42,15,44,17,46,19,48,21,50,52,54,56,58,60,23,62,25,64,27,66,29,68, %U A351998 31,70,72,74,76,78,80,33,82,35,84,37,86,39,88,41,90,92,94,96,98,100,43,102,45,104,47,106,49 %N A351998 A chain reaction sequence: a digit d1 from a(n) is expelled towards a(n+1) where it hits a digit d2 [from a(n+1)] and replaces it; d2 in turn is expelled towards a(n+2), hits a digit d3 there and replaces it; d3 in turn is expelled towards a(n+3), hits a digit there, and replaces it; d4 is expelled... etc. At the end of the chain reaction, only even numbers will be left. This is the lexicographically earliest sequence of distinct positive integers with this property. %C A351998 The sequence is a permutation of the integers > 0. %H A351998 Eric Angelini, <a href="http://cinquantesignes.blogspot.com/2022/02/a-chain-reaction-producing-primes.html">A chain reaction producing primes</a>, personal blog of the author, Feb. 2022. %e A351998 1 is expelled from a(1) = 1 and hits the 1 of a(2) = 10, "turning" this integer into 10, an even number; %e A351998 1 is expelled from a(2) = 10 and hits the 1 of a(3) = 12, "turning" this integer into 12, an even number; %e A351998 1 is expelled from a(3) = 12 and hits the 1 of a(4) = 14, "turning" this integer into 14, an even number; %e A351998 1 is expelled from a(4) = 14 and hits the 1 of a(5) = 16, "turning" this integer into 16, an even number; %e A351998 1 is expelled from a(5) = 16 and hits the 1 of a(6) = 18, "turning" this integer into 18, an even number; %e A351998 1 is expelled from a(6) = 18 and hits the 2 of a(7) = 20, turning this integer into 10, an even number; %e A351998 2 is expelled from a(7) = 20 and hits the 2 of a(8) = 2, "turning" this integer into 2, an even number; %e A351998 2 is expelled from a(8) = 2 and hits the 3 of a(9) = 3, turning this integer into 2, an even number; %e A351998 3 is expelled from a(9) = 3 and hits the leftmost 2 of a(10) = 22, turning this integer into 32, an even number; etc. %Y A351998 Cf. A351996 (prime numbers left), A351997 (odd numbers left), A351999 (Fibonacci numbers left), A352000 (square numbers left). %K A351998 base,nonn %O A351998 1,2 %A A351998 _Eric Angelini_ ansd _Carole Dubois_, Feb 27 2022