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 A113402 #48 Feb 16 2025 08:32:59
%S A113402 1,1,1,2,2,2,4,4,4,4,8,8,8,8,8,16,16,16,16,16,16,32,32,32,32,32,32,32,
%T A113402 64,64,64,64,64,64,64,64,128,128,128,128,128,128,128,128,128,256,256,
%U A113402 256,256,256,256,256,256,256,256,512,512,512,512,512,512,512,512,512
%N A113402 Algebraic degree of cos(Pi/n) for constructible n-gons (A003401).
%C A113402 a(n) is always a power of 2.
%C A113402 It would appear that a(n) <= a(n+1) and that for a(n)=2^k, the count for k beginning with 0 is 3, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, ...; or that the count for k is k+2 for k > 0. - _Robert G. Wilson v_, Jul 31 2014
%C A113402 Apparently v_2(a(n)) = A052146(n-1) for n >= 2 where v_2 is the 2-adic valuation. - _Joerg Arndt_, Jul 29 2014 [incorrect for n >= 561, _Joerg Arndt_, Mar 03 2019]
%H A113402 Robert G. Wilson v, <a href="/A113402/b113402.txt">Table of n, a(n) for n = 1..1632</a>
%H A113402 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TrigonometryAngles.html">Trigonometry Angles</a>
%t A113402 f[n_] := Exponent[MinimalPolynomial[Cos[Pi/n]][x], x]; Table[ f@ n, {n, Select[ Range@ 1300, IntegerQ[ Log[2, EulerPhi[#]]] &]}] (* _Robert G. Wilson v_, Jul 28 2014 *)
%t A113402 A092506 = {2, 3, 5, 17, 257, 65537}; s = Sort[Times @@@ Subsets@ A092506]; mx = 2500; t = Union@ Flatten@ Table[(2^n)*s[[i]], {i, 64}, {n, 0, Log2[mx/s[[i]]]}]; f[n_] := EulerPhi[ 2n]/2; f[1] = 1; f@# & /@ t (* _Robert G. Wilson v_, Jul 28 2014 *)
%Y A113402 Cf. A000217, A002024, A003401, A055034, A113401.
%K A113402 nonn,easy,nice
%O A113402 1,4
%A A113402 _Eric W. Weisstein_, Oct 28 2005