%I #15 Jan 21 2021 10:04:12
%S 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 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 9,8,2,9,2,8,9,5,5,9,8,2,9,2,8,9,5,5,9,8,2,9
%N Digital root of 2*n^2.
%C Period 9: repeat [2, 8, 9, 5, 5, 9, 8, 2, 9].
%C 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 <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 a(n) = A010888(A001105(n)).
%e For n=5, 2*5^2 = 50 and digital root is 5, so a(5) = 5.
%o (PARI) dr(n) = if(n, (n-1)%9+1); \\ A010888
%o a(n) = dr(2*n^2); \\ _Michel Marcus_, Jan 21 2021
%Y Cf. A001105, A010888, A056992.
%K nonn,base,easy
%O 1,1
%A _Radaev Nikita_, Jan 10 2021