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 A356860 #11 Jul 20 2025 13:52:24
%S A356860 1,1,1,1,2,3,4,4,5,6,7,9,10,11,12,13,15,16,17,19,20,22,23,24,26,27,29,
%T A356860 30,32,33,35,37,38,40,41,43,45,46,48,50,51,53,55,57,58,60,62,64,65,67,
%U A356860 69,71,73,74,76,78,80,82,84,85,87,89,91,93,95,97,99,101,103
%N A356860 a(n) is the number of digits in the product of the first n numbers not divisible by 5.
%H A356860 Harvey P. Dale, <a href="/A356860/b356860.txt">Table of n, a(n) for n = 0..1000</a>
%F A356860 a(n) = A055642(A356858(n)).
%t A356860 Table[Length[IntegerDigits[Product[Floor[(5i-1)/4], {i,n}]]], {n,0,68}]
%t A356860 Join[{1},IntegerLength/@FoldList[Times,Table[If[Mod[n,5]==0,Nothing,n],{n,0,100}]]] (* _Harvey P. Dale_, Jul 20 2025 *)
%o A356860 (Python)
%o A356860 from math import prod
%o A356860 def a(n): return len(str(prod((5*k-1)//4 for k in range(1, n+1))))
%o A356860 print([a(n) for n in range(69)]) # _Michael S. Branicky_, Sep 01 2022
%Y A356860 Cf. A047201, A055642, A356858.
%Y A356860 Cf. A356859 (number of zero digits), A356861 (number of nonzero digits).
%K A356860 nonn,base
%O A356860 0,5
%A A356860 _Stefano Spezia_, Sep 01 2022