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 A273005 #17 Feb 16 2025 08:33:34
%S A273005 0,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10,11,3,4,5,6,7,8,9,10,11,12,4,5,
%T A273005 6,7,8,9,10,11,12,13,5,6,7,8,9,10,11,12,13,14,6,7,8,9,10,11,12,13,14,
%U A273005 15,7,8,9,10,11,12,13,14,15,16,8,9,10,11,12,13,14,15,16,17,9,10,11,12,13,14,15,16,17,18,10,11,12,13,14,15,16,17,18,19,3
%N A273005 Sum of coefficients in the hereditary representation of n in base 10.
%H A273005 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HereditaryRepresentation.html">Hereditary Representation.</a>
%F A273005 If n = Sum_{j=1..k} d_j*10^(e_j) where 0 <= e_1 < ... < e_k and 1 <= d_j <= 9, then a(n) = Sum_{j=1..k} (d_j + a(e_j)). - _Pontus von Brömssen_, Sep 17 2020
%e A273005 266 = 6 + 6*10^1 + 2*10^2 which can be represented as [6, [6, [1]], [2, [2]]], therefore a(266) = 6 + 6 + 1 + 2 + 2 = 17.
%o A273005 (PARI) (hr(n,b=10)=if(1<#n=digits(n,b),my(v=if(n[#n],[n[#n]],[]));forstep(i=#n-1,1,-1,n[i]&&v=concat(v,[[n[i],hr(#n-i,b)]]));v,n));(cc(v)=if(type(v)=="t_VEC",sum(i=1,#v,cc(v[i])),v)); a(n)=cc(hr(n,10))
%o A273005 (Python)
%o A273005 def A273005(n):
%o A273005 s=str(n)[::-1]
%o A273005 return sum(int(s[i])+A273005(i) for i in range(len(s)) if s[i]!='0') # _Pontus von Brömssen_, Sep 17 2020
%Y A273005 Cf. A273004, A056004, A222112.
%K A273005 nonn,base
%O A273005 0,3
%A A273005 _M. F. Hasler_, May 12 2016