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 A128212 #26 Sep 26 2023 21:54:21
%S A128212 1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0,2,4,6,8,1,3,5,7,9,0,3,6,9,3,
%T A128212 6,9,3,6,9,0,4,8,3,7,2,6,10,5,9,0,5,1,6,2,7,3,8,4,9,0,6,3,9,6,3,9,6,
%U A128212 12,9,0,7,5,3,10,8,6,13,11,9,0,8,7,6,5,4,12,11,10,9,0,9,9,9,9,9,9,9,9,9,0
%N A128212 a(n) = Sum_digits(p), where p is the product of the digits of n.
%C A128212 The sequence grows very slowly. For n <= 10000 the maximal value is 27.
%H A128212 Marius A. Burtea, <a href="/A128212/b128212.txt">Table of n, a(n) for n = 1..6000</a>
%F A128212 a(n) = A007953(A007954(n)). - _Michel Marcus_, Jun 07 2019 [Corrected by _Sean A. Irvine_, Sep 26 2023]
%e A128212 a(73) = 3 because 7*3 = 21 and 2+1 = 3.
%p A128212 P:=proc(n) local i,k,w; for i from 1 by 1 to n do w:=1;k:=i; while k>0 do w:=w*(k-(trunc(k/10)*10)); k:=trunc(k/10); od; k:=w; w:=0; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; print(w); od; end: P(100);
%t A128212 Table[Total[IntegerDigits[Times@@IntegerDigits[n]]],{n,100}] (* _Harvey P. Dale_, Feb 08 2013 *)
%o A128212 (Magma) [&+Intseq((&*(Intseq(n)))):n in [1..100]]; // _Marius A. Burtea_, Jun 06 2019
%o A128212 (PARI) a(n) = sumdigits(vecprod(digits(n))); \\ _Michel Marcus_, Jun 07 2019
%Y A128212 Cf. A007953, A007954.
%K A128212 easy,nonn,base
%O A128212 1,2
%A A128212 _Paolo P. Lava_ and _Giorgio Balzarotti_, May 03 2007