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 A304373 #12 Feb 16 2025 08:33:54
%S A304373 19999999999999999999999,28999999999999999999999,
%T A304373 29899999999999999999999,29989999999999999999999,
%U A304373 29998999999999999999999,29999899999999999999999,29999989999999999999999,29999998999999999999999,29999999899999999999999,29999999989999999999999
%N A304373 Numbers n with additive persistence = 4.
%H A304373 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AdditivePersistence.html">Additive Persistence</a>
%F A304373 A031286(a(n)) = 4.
%e A304373 Repeatedly taking the sum of digits starting with 19999999999999999999999 gives 199, 19, 10 and 1. There are four steps, so the additive persistence is 4 and 19999999999999999999999 is a member.
%t A304373 Take[ Sort@ Flatten[ (FromDigits /@ Permutations@#) & /@ IntegerPartitions[ 199, {23}, Range@ 9]], 10000] (* first 10000 terms, _Giovanni Resta_, May 29 2018 *)
%o A304373 (PARI) nb(n) = {my(nba = 0); while (n > 9, n = sumdigits(n); nba++); nba;}
%o A304373 isok(n) = nb(n) == 4; \\ _Michel Marcus_, May 29 2018
%Y A304373 Cf. A031286.
%Y A304373 Cf. Numbers with additive persistence k: A304366 (k=1), A304367 (k=2), A304368 (k=3).
%K A304373 nonn,base
%O A304373 1,1
%A A304373 _Jaroslav Krizek_, May 28 2018