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 A254373 #14 Aug 26 2015 17:09:06
%S A254373 1,5,4,7,5,7,4,5,1,1,5,4,7,5,7,4,5,1,1,5,4,7,5,7,4,5,1,1,5,4,7,5,7,4,
%T A254373 5,1,1,5,4,7,5,7,4,5,1,1,5,4,7,5,7,4,5,1,1,5,4,7,5,7,4,5,1,1,5,4,7,5,
%U A254373 7,4,5,1,1,5,4,7,5,7,4,5,1,1,5,4,7,5
%N A254373 Digital roots of centered square numbers (A001844).
%C A254373 The sequence is periodic with period 9.
%H A254373 Colin Barker, <a href="/A254373/b254373.txt">Table of n, a(n) for n = 1..1000</a>
%H A254373 <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 A254373 a(n) = A010888(A001844(n)).
%F A254373 a(n) = a(n-9).
%F A254373 G.f.: -x*(x^8+5*x^7+4*x^6+7*x^5+5*x^4+7*x^3+4*x^2+5*x+1) / ((x-1)*(x^2+x+1)*(x^6+x^3+1)).
%e A254373 a(3) = 4 because the 3rd centered square number is 13, the digital root of which is 4.
%t A254373 FixedPoint[Plus @@ IntegerDigits[#] &, #] & /@ Table[2 n (n + 1) + 1, {n, 0, 80}] (* _Michael De Vlieger_, Feb 01 2015 *)
%t A254373 LinearRecurrence[{0, 0, 0, 0, 0, 0, 0, 0, 1},{1, 5, 4, 7, 5, 7, 4, 5, 1},86] (* _Ray Chandler_, Aug 26 2015 *)
%o A254373 (PARI) m=4; vector(200, n, (m*n*(n-1)/2)%9+1)
%Y A254373 Cf. A001844, A010888.
%K A254373 nonn,easy,base
%O A254373 1,2
%A A254373 _Colin Barker_, Jan 29 2015