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 A303296 #35 Nov 13 2021 13:55:07
%S A303296 1,7,9,4,4,9,7,1,9,1,7,9,4,4,9,7,1,9,1,7,9,4,4,9,7,1,9,1,7,9,4,4,9,7,
%T A303296 1,9,1,7,9,4,4,9,7,1,9,1,7,9,4,4,9,7,1,9,1,7,9,4,4,9,7,1,9,1,7,9,4,4,
%U A303296 9,7,1,9,1,7,9,4,4,9,7,1,9,1,7,9,4,4,9,7,1,9
%N A303296 Digital roots of fourth powers A000583.
%C A303296 This sequence is related to A056992, the digital roots of the squares, and also presents a period of 9, in this case repeat [1, 7, 9, 4, 4, 9, 7, 1, 9].
%C A303296 a(n) = 9 if n is a multiple of 3.
%C A303296 Replace 4 with 7 and 7 with 4 in A056992. - _Omar E. Pol_, Apr 21 2018
%C A303296 a(n) is also the decimal expansion of 598165730/333333333. - _Enrique Pérez Herrero_, Nov 13 2021
%H A303296 I. Izmirli, <a href="https://doi.org/10.4236/apm.2014.46039">On Some Properties of Digital Roots</a>, Advances in Pure Mathematics, Vol. 4 No. 6 (2014), Article ID:47285.
%H A303296 <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 A303296 a(n) = A010888(A000583(n)) = a(n - 9).
%t A303296 Table[FixedPoint[Total[IntegerDigits[#]] &, n^4], {n, 90}]
%o A303296 (PARI) a(n) = (n^4-1)%9+1; \\ _Michel Marcus_, Apr 22 2018
%Y A303296 Cf. A000583, A010888, A056992.
%K A303296 nonn,base,easy
%O A303296 1,2
%A A303296 _Gaston Maire_ and students, Apr 21 2018