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 A364811 #27 Sep 17 2023 18:29:50
%S A364811 1,2,2,2,2,4,6,10,18,36,70,138,274,548,1094,2186,4370,8740,17478,
%T A364811 34954,69906,139812,279622,559242,1118482,2236964,4473926
%N A364811 Number of distinct residues x^4 (mod 2^n), x=0..2^n-1.
%C A364811 For n>=4, A319281(a(n)) == 2^n + [(n mod 4)>0].
%C A364811 It appears that for n>4: a(n)=2*a(n-1)-2*[(n mod 4)==2]; a(n) = ceiling(2^n/15) - [(n mod 4)==0] + 1.
%t A364811 a[n_]:=CountDistinct[Table[PowerMod[x-1, 4, 2^(n-1)], {x, 1, 2^(n-1)}]]; Array[a, 24]
%o A364811 (PARI) a(n) = #Set(vector(2^(n-1), x, Mod(x-1, 2^(n-1))^4))
%o A364811 (Python)
%o A364811 def A364811(n): return len({pow(x,4,1<<n) for x in range(1<<n)}) # _Chai Wah Wu_, Sep 17 2023
%Y A364811 Cf. A319281, A023105, A046630, A365103.
%K A364811 nonn,more
%O A364811 0,2
%A A364811 _Albert Mukovskiy_, Sep 14 2023