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 A343586 #35 Sep 18 2021 00:39:38 %S A343586 35,3050,300500,30005000,3000050000,300000500000,30000005000000, %T A343586 3000000050000000,300000000500000000,30000000005000000000, %U A343586 3000000000050000000000,300000000000500000000000,30000000000005000000000000,3000000000000050000000000000 %N A343586 a(n) = the sum of all the multiples of 2 or 5 less than or equal to 10^n. %H A343586 Nicolo Sartori di Borgoricco, <a href="/A343586/a343586.pdf">Proof that formula is correct</a> %H A343586 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (110,-1000). %F A343586 a(n) = 3*10^(2*n-1) + 5*10^(n-1). %F A343586 G.f.: 5*x*(7 - 160*x)/(1 - 110*x + 1000*x^2). - _Stefano Spezia_, Apr 21 2021 %F A343586 a(n) = 110*a(n-1)-1000*a(n-2). - _Wesley Ivan Hurt_, Apr 26 2021 %e A343586 a(1) = 2 + 5 + 4 + 6 + 8 + 10 = 3*10^(2*1-1) + 5*10^(1-1) = 35. %Y A343586 Cf. A065502 (multiples of 2 or 5). %K A343586 nonn,easy %O A343586 1,1 %A A343586 _Nicolo Sartori di Borgoricco_, Apr 20 2021