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 A216326 #8 Sep 12 2023 13:09:58 %S A216326 1,1,2,2,2,4,4,3,2,4,4,6,6,4,2,4,2,8,4,4,9,4,2,6,10,6,4,2,8,8,6,4,6,4, %T A216326 4,6,8,5,2,4,2,12,4,12,6,6,8,4,2,8,6,4,16,4,8,2,4,8,8,12,4,4,6,4,12,4, %U A216326 8,16,2,8,10,2,4,8,8,2,4,12,12,12,4,16,4,16,4,4,12,12,8,8,2 %N A216326 Number of divisors of the degree of the minimal polynomial of 2*cos(Pi/prime(n)), with prime = A000040, n >= 1. %C A216326 See a comment on A216325 on the degree delta(n) = A055034(n) of the polynomial C(n,x) of 2*cos(Pi/n) (coefficients in A187360), Here n is prime. %C A216326 For p prime, delta(p) = (p - 1)/2 if p > 2 and 1 if p = 2. a(n) is the number of divisors of delta(prime(n)), with prime(n) = A000040(n). %C A216326 a(n) is also the number of distinct Modd p orders, p = prime, in row prime(n) of the table A216320. (For Modd n see a comment on A203571). %C A216326 See also A008328 for the mod p analog of this sequence. %F A216326 a(n) = tau(delta(prime(n))), n>=1, with tau = A000005 (number of divisors), delta = A055034 and prime = A000040. %e A216326 a(6) = 4 because prime(6) = 13, and row n=13 of A216320 is [1 3 2 6 3 6] with 4 distinct numbers (Modd 13 orders). %o A216326 (PARI) delta(n) = if (n==1, 1, eulerphi(2*n)/2); \\ A055034 %o A216326 a(n) = numdiv(delta(prime(n))); \\ _Michel Marcus_, Sep 12 2023 %Y A216326 Cf. A000005, A055034, A000040. %Y A216326 Cf. A187360, A216320, A216325, A008328 (mod p analog). %K A216326 nonn %O A216326 1,3 %A A216326 _Wolfdieter Lang_, Sep 27 2012