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 A385978 #22 Jul 20 2025 19:15:48
%S A385978 10,20,30,40,50,60,70,80,90,200,110,120,130,140,150,160,170,180,190,
%T A385978 400,210,220,230,240,250,260,270,280,290,600,310,320,330,340,350,360,
%U A385978 370,380,390,800,410,420,430,440,450,460,470,480,490,1000,510,520,530,540
%N A385978 Number of trailing zeros in (10*n)^(10*n).
%H A385978 Marco Ripà, <a href="https://arxiv.org/abs/2402.07929">Congruence speed of tetration bases ending with 0</a>, arXiv:2402.07929 [math.NT], 2024.
%F A385978 a(n) = 10*n*(A122840(n) + 1).
%e A385978 a(2) = 20 since 20^(10*2) = 104857600000000000000000000 has 20 trailing zeros.
%t A385978 a[n_] := 10 n (IntegerExponent[n, 10] + 1) Table[a[n], {n, 1, 30}]
%o A385978 (PARI) a(n) = 10*n*(valuation(n,10)+1); \\ _Michel Marcus_, Jul 14 2025
%Y A385978 Cf. A007814, A011557, A027868, A112765, A122840, A356946.
%K A385978 nonn,base,easy
%O A385978 1,1
%A A385978 _Marco Ripà_, Jul 13 2025