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 A104720 #34 Jun 20 2021 20:02:26
%S A104720 1,11,112,1122,11223,112233,1122334,11223344,112233445,1122334455,
%T A104720 11223344556,112233445566,1122334455667,11223344556677,
%U A104720 112233445566778,1122334455667788,11223344556677889,112233445566778899,1122334455667789000,11223344556677890010,112233445566778900111,1122334455667789001121
%N A104720 Expansion of 1/((1-x)(1-x^2)(1-10x)).
%C A104720 Partial sums of A056830(n+1).
%H A104720 Seiichi Manyama, <a href="/A104720/b104720.txt">Table of n, a(n) for n = 0..999</a>
%H A104720 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (11,-9,-11,10).
%F A104720 a(n) = 1000*10^n/891 + (-1)^n/44 - (18n+47)/324.
%F A104720 a(n) = floor((2*10^(n+3) - 99n)/1782). - _Hieronymus Fischer_, Dec 05 2006
%F A104720 a(n) = 10*a(n-1) + (2*n + 3 + (-1)^n)/4, a(0)=1, a(1)=11. - _Vincenzo Librandi_, Mar 22 2011
%e A104720 From _Seiichi Manyama_, Sep 29 2018: (Start)
%e A104720 1 * 8 + 0 = 8;
%e A104720 11 * 8 + 1 = 89;
%e A104720 112 * 8 + 1 = 897;
%e A104720 1122 * 8 + 2 = 8978;
%e A104720 11223 * 8 + 2 = 89786;
%e A104720 112233 * 8 + 3 = 897867;
%e A104720 1122334 * 8 + 3 = 8978675;
%e A104720 11223344 * 8 + 4 = 89786756;
%e A104720 112233445 * 8 + 4 = 897867564;
%e A104720 1122334455 * 8 + 5 = 8978675645;
%e A104720 11223344556 * 8 + 5 = 89786756453;
%e A104720 112233445566 * 8 + 6 = 897867564534;
%e A104720 1122334455667 * 8 + 6 = 8978675645342;
%e A104720 11223344556677 * 8 + 7 = 89786756453423;
%e A104720 112233445566778 * 8 + 7 = 897767564534231;
%e A104720 1122334455667788 * 8 + 8 = 8978675645342312;
%e A104720 11223344556677889 * 8 + 8 = 89786756453423120;
%e A104720 112233445566778899 * 8 + 9 = 897867564534231201.
%e A104720 1 * 9 + 1 = 10;
%e A104720 11 * 9 + 2 = 101;
%e A104720 112 * 9 + 2 = 1010;
%e A104720 1122 * 9 + 3 = 10101;
%e A104720 11223 * 9 + 3 = 101010;
%e A104720 112233 * 9 + 4 = 1010101;
%e A104720 1122334 * 9 + 4 = 10101010;
%e A104720 11223344 * 9 + 5 = 101010101;
%e A104720 112233445 * 9 + 5 = 1010101010;
%e A104720 1122334455 * 9 + 6 = 10101010101;
%e A104720 11223344556 * 9 + 6 = 101010101010;
%e A104720 112233445566 * 9 + 7 = 1010101010101;
%e A104720 1122334455667 * 9 + 7 = 10101010101010;
%e A104720 11223344556677 * 9 + 8 = 101010101010101;
%e A104720 112233445566778 * 9 + 8 = 1010101010101010;
%e A104720 1122334455667788 * 9 + 9 = 10101010101010101;
%e A104720 11223344556677889 * 9 + 9 = 101010101010101010;
%e A104720 112233445566778899 * 9 + 10 = 1010101010101010101. (End)
%p A104720 seq(coeff(series(((1-x)*(1-x^2)*(1-10*x))^(-1),x,n+1), x, n), n = 0 .. 25); # _Muniru A Asiru_, Sep 29 2018
%t A104720 a[n_]:=1000*10^n/891 + (-1)^n/44 - (18*n + 47)/324 ; Array[a,50,0] (* or *)
%t A104720 a[n_]:=Floor[(2*10^(n + 3) - 99*n)/1782]; Array[a,50,0] (* _Stefano Spezia_, Sep 01 2018 *)
%t A104720 LinearRecurrence[{11,-9,-11,10},{1,11,112,1122},30] (* _Harvey P. Dale_, Jun 20 2021 *)
%o A104720 (GAP) List([0..25],n->1000*10^n/891+(-1)^n/44-(18*n+47)/324); # _Muniru A Asiru_, Sep 29 2018
%Y A104720 Cf. A056830, A294328, A294344.
%K A104720 easy,nonn
%O A104720 0,2
%A A104720 _Paul Barry_, Mar 20 2005