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 A340536 #15 Jan 21 2021 10:04:12 %S A340536 2,8,9,5,5,9,8,2,9,2,8,9,5,5,9,8,2,9,2,8,9,5,5,9,8,2,9,2,8,9,5,5,9,8, %T A340536 2,9,2,8,9,5,5,9,8,2,9,2,8,9,5,5,9,8,2,9,2,8,9,5,5,9,8,2,9,2,8,9,5,5, %U A340536 9,8,2,9,2,8,9,5,5,9,8,2,9,2,8,9,5,5,9,8,2,9 %N A340536 Digital root of 2*n^2. %C A340536 Period 9: repeat [2, 8, 9, 5, 5, 9, 8, 2, 9]. %C A340536 This sequence is also right if digital root of factor in "2*n^2" is 2 (for example, "11*n^2", "20*n^2", "29*n^2", etc.) %H A340536 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,1). %F A340536 a(n) = A010888(A001105(n)). %e A340536 For n=5, 2*5^2 = 50 and digital root is 5, so a(5) = 5. %o A340536 (PARI) dr(n) = if(n, (n-1)%9+1); \\ A010888 %o A340536 a(n) = dr(2*n^2); \\ _Michel Marcus_, Jan 21 2021 %Y A340536 Cf. A001105, A010888, A056992. %K A340536 nonn,base,easy %O A340536 1,1 %A A340536 _Radaev Nikita_, Jan 10 2021