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 A064756 #35 Sep 09 2024 11:59:53
%S A064756 9,199,2999,39999,499999,5999999,69999999,799999999,8999999999,
%T A064756 99999999999,1099999999999,11999999999999,129999999999999,
%U A064756 1399999999999999,14999999999999999,159999999999999999,1699999999999999999,17999999999999999999,189999999999999999999,1999999999999999999999
%N A064756 a(n) = n*10^n - 1.
%H A064756 Vincenzo Librandi, <a href="/A064756/b064756.txt">Table of n, a(n) for n = 1..1000</a>
%H A064756 Paul Leyland, <a href="https://web.archive.org/web/20120204131613/http://www.leyland.vispa.com/numth/factorization/cullen_woodall/cw.htm">Factors of Cullen and Woodall numbers</a>.
%H A064756 Paul Leyland, <a href="https://web.archive.org/web/20120204131629/http://www.leyland.vispa.com/numth/factorization/cullen_woodall/gcw.htm">Generalized Cullen and Woodall numbers</a>.
%H A064756 Amelia Carolina Sparavigna, <a href="https://doi.org/10.18483/ijSci.2188">Some Groupoids and their Representations by Means of Integer Sequences</a>, International Journal of Sciences (2019) Vol. 8, No. 10.
%H A064756 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (21,-120,100).
%F A064756 From _Elmo R. Oliveira_, Sep 07 2024: (Start)
%F A064756 G.f.: x*(100*x^2 - 10*x - 9)/((x - 1)*(10*x - 1)^2).
%F A064756 E.g.f.: 1 + exp(x)*(10*x*exp(9*x) - 1).
%F A064756 a(n) = 21*a(n-1) - 120*a(n-2) + 100*a(n-3) for n > 3.
%F A064756 a(n) = A126431(n) - 1 = A064748(n) - 2. (End)
%p A064756 k:= 10; f:= gfun:-rectoproc({1 + (k-1)*n + k*n*a(n-1) - (n-1)*a(n) = 0, a(1) = k-1}, a(n), remember): map(f, [$1..20]); # _Georg Fischer_, Feb 19 2021
%t A064756 Array[# 10^# - 1 &, 18] (* _Michael De Vlieger_, Jan 14 2020 *)
%o A064756 (Magma) [ n*10^n-1: n in [1..20]]; // _Vincenzo Librandi_, Sep 16 2011
%Y A064756 Cf. for a(n) = n*k^n - 1: -A000012 (k=0), A001477 (k=1), A003261 (k=2), A060352 (k=3), A060416 (k=4), A064751 (k=5), A064752 (k=6), A064753 (k=7), A064754 (k=8), A064755 (k=9), this sequence (k=10), A064757 (k=11), A064758 (k=12).
%Y A064756 Cf. A064748, A126431.
%K A064756 nonn,easy
%O A064756 1,1
%A A064756 _N. J. A. Sloane_, Oct 19 2001