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 A299871 #13 Feb 25 2018 21:44:06
%S A299871 8,80,792,7927,79272,792713,7927135,79271352,792713513,7927135135,
%T A299871 79271351350,792713513502,7927135135013,79271351350135,
%U A299871 792713513501345,7927135135013455,79271351350134552,792713513501345513,7927135135013455135,79271351350134551344,792713513501345513442,7927135135013455134424
%N A299871 The sum of the first n terms of the sequence is the concatenation of the first n digits of the sequence, and a(1) = 8.
%C A299871 The sequence starts with a(1) = 8 and is always extended with the smallest integer not yet present in the sequence and not leading to a contradiction.
%H A299871 Jean-Marc Falcoz, <a href="/A299871/b299871.txt">Table of n, a(n) for n = 1..300</a>
%F A299871 a(n) = c(n) - c(n-1), where c(n) = concatenation of the first n digits, c(n) ~ 0.88*10^n, a(n) ~ 0.79*10^n. See A300000 for the proof. - _M. F. Hasler_, Feb 22 2018
%e A299871 8 + 80 = 88 which is the concatenation of 8 and 8.
%e A299871 8 + 80 + 792 = 880 which is the concatenation of 8, 8 and 0.
%e A299871 8 + 80 + 792 + 7927 = 8807 which is the concatenation of 8, 8, 0 and 7.
%e A299871 From n = 3 on, a(n) can be computed directly as c(n) - c(n-1), cf. formula: a(3) = 880 - 88 = 792, a(4) = 8807 - 880 = 7927, etc. - _M. F. Hasler_, Feb 22 2018
%o A299871 (PARI) a(n,show=1,a=8,c=a,d=[a])={for(n=2,n,show&&print1(a",");a=-c+c=c*10+d[1];d=concat(d[^1],if(n>2,digits(a))));a} \\ _M. F. Hasler_, Feb 22 2018
%Y A299871 A300000 is the lexicographically first sequence of this type, with a(1) = 1.
%Y A299871 Cf. A299865, ..., A299872 for variants with a(1) = 2, ..., 9.
%K A299871 nonn,base
%O A299871 1,1
%A A299871 _Eric Angelini_ and _Jean-Marc Falcoz_, Feb 21 2018