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 A235699 #23 Apr 02 2020 11:43:50
%S A235699 0,1,3,7,15,21,23,27,35,41,43,47,55,61,63,67,75,81,83,87,95,101,103,
%T A235699 107,115,121,123,127,135,141,143,147,155,161,163,167,175,181,183,187,
%U A235699 195,201,203,207,215,221,223,227,235,241,243,247,255,261,263,267,275,281,283,287,295,301,303,307,315,321,323,327,335,341,343,347,355
%N A235699 a(n+1) = a(n) + (a(n) mod 10) + 1, a(0) = 0.
%C A235699 Instead of (a(n) mod 10) one might say "the last (decimal) digit of a(n)".
%C A235699 Apart from the initial term, the first differences form the periodic sequence (2,4,8,6)[repeated].
%C A235699 Without the final "+ 1" and starting with 1, one gets A102039: Indeed, the last digit cycles through 2,4,8,6 and therefore the sequence never becomes constant.
%H A235699 Harvey P. Dale, <a href="/A235699/b235699.txt">Table of n, a(n) for n = 0..1000</a>
%H A235699 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,2,-1).
%F A235699 a(n) = 5*n-6+cos(n*Pi/2)+2*sin(n*Pi/2), for n>0. - _Giovanni Resta_, Jan 15 2014
%F A235699 From _Colin Barker_, Jan 16 2014: (Start)
%F A235699 a(n) = -6+(1/2+i)*(-i)^n+(1/2-i)*i^n+5*n for n>0 where i=sqrt(-1).
%F A235699 a(n) = 2*a(n-1)-2*a(n-2)+2*a(n-3)-a(n-4) for n>4.
%F A235699 G.f.: x*(5*x^3+3*x^2+x+1) / ((x-1)^2*(x^2+1)). (End)
%t A235699 NestList[#+Mod[#,10]+1&,0,80] (* or *) Join[{0},LinearRecurrence[{2,-2,2,-1},{1,3,7,15},80]] (* _Harvey P. Dale_, Dec 21 2014 *)
%o A235699 (PARI) print1(a=0);for(i=1,99,print1(","a+=a%10+1))
%Y A235699 Cf. A102039, A235698, A045844.
%K A235699 nonn,base,easy
%O A235699 0,3
%A A235699 _M. F. Hasler_, Jan 14 2014