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 A139280 #39 Apr 04 2025 12:28:59
%S A139280 9,99,189,279,369,459,549,639,729,819,909,999,1089,1179,1269,1359,
%T A139280 1449,1539,1629,1719,1809,1899,1989,2079,2169,2259,2349,2439,2529,
%U A139280 2619,2709,2799,2889,2979,3069,3159,3249,3339,3429,3519,3609,3699,3789,3879,3969
%N A139280 a(n) = 90*n - 81.
%C A139280 Multiples of 9 with final digit 9.
%H A139280 Vincenzo Librandi, <a href="/A139280/b139280.txt">Table of n, a(n) for n = 1..2000</a>
%H A139280 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A139280 a(n) = a(n-1) + 90.
%F A139280 From _G. C. Greubel_, Jul 18 2017: (Start)
%F A139280 G.f.: 9*(19*x-9)/(x-1)^2.
%F A139280 E.g.f.: 81 + 9*(10*x - 9)*exp(x). (End) [G.f. corrected by _Georg Fischer_, May 12 2019]; [E.g.f. corrected by _Elmo R. Oliveira_, Apr 04 2025]
%F A139280 From _Elmo R. Oliveira_, Apr 04 2025: (Start)
%F A139280 a(n) = 9*A017281(n-1) = 3*A139222(n).
%F A139280 a(n) = 2*a(n-1) - a(n-2) for n > 2. (End)
%t A139280 Table[90*n-81, {n, 0, 50}] (* _G. C. Greubel_, Jul 18 2017 *)
%o A139280 (Magma) [90*n-81: n in [1..50]]; // _Vincenzo Librandi_, Jun 19 2011
%o A139280 (PARI) for(n=1, 1e2, a=90*n-81; print1(a, ", ")) \\ _Felix Fröhlich_, Jul 07 2014
%Y A139280 Subsequence of A034709, together with A017281, A017293, A139222, A139245, A017329, A139249, A139264 and A139279.
%Y A139280 Cf. A017281, A139222.
%K A139280 easy,nonn
%O A139280 1,1
%A A139280 _Odimar Fabeny_, Jun 06 2008
%E A139280 More terms from _Reinhard Zumkeller_, Jun 22 2008