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 A215028 #11 Jan 22 2021 15:44:34
%S A215028 1,20,12,31,23,42,34,53,45,64,1046,165,1147,266,1248,367,1349,468,
%T A215028 1450,569,1551,670,1652,771,1753,872,1854,973,1955,1074,2056,1175,
%U A215028 2157,1276,2258,1377,2359,1478,2460,1579,2561,1680,2662,1781,2763,1882,2864,1983
%N A215028 a(1) = 1; for n >= 1, a(n+1) = (concatenation of n+1 and n) - a(n).
%C A215028 A variation of A215027.
%p A215028 f:=proc(i) (i+1)*10^(1+floor(evalf(log10(i))))+i; end: # A127423
%p A215028 a:=proc(n) option remember; global f; if n=1 then 1 else f(n-1)-a(n-1); fi; end;
%o A215028 (PARI) A215028(n, print_all=0)={my(a=1); for(n=1, n-1, print_all & print1(a","); a=(n+1)*10^#Str(n)+n-a); a} \\ _M. F. Hasler_, Aug 23 2012
%Y A215028 Cf. A215027, A127423.
%K A215028 nonn,base
%O A215028 1,2
%A A215028 _N. J. A. Sloane_, Aug 04 2012