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 A327790 #11 Mar 09 2021 02:55:16
%S A327790 1,1,1,1,2,1,2,1,2,2,4,1,4,2,2,2,8,2,6,2,2,4,10,1,8,4,6,2,12,2,8,4,4,
%T A327790 8,4,2,12,6,4,2,16,2,12,4,4,10,22,2,12,8,8,4,24,6,8,2,6,12,28,2,16,8,
%U A327790 4,8,8,4,20,8,10,4,24,2,24,12,8,6,8,4,24,4,18,16,40,2,16,12
%N A327790 Decompose the multiplicative group of integers modulo n as a product of cyclic groups C_{k_1} X C_{k_2} X ... X C_{k_r}, where k_i > 1, k_i divides k_j for i < j; then a(n) = Product_{i=1..r} phi(k_i), phi = A000010.
%C A327790 Related to A327791, which concerns the number of ways, up to the order, of decomposing the multiplicative group of integers modulo n to the inner direct product of cyclic subgroups. See the formula for it there.
%C A327790 Note that the choice of (k_1, k_2, ..., k_r) does not affect the result. For example, (Z/35Z)* = C_2 X C_12 = C_4 X C_6 = C_2 X C_2 X C_12, and we have phi(2)*phi(12) = phi(4)*phi(6) = phi(2)*phi(2)*phi(12) = 4 = a(35).
%H A327790 Jianing Song, <a href="/A327790/b327790.txt">Table of n, a(n) for n = 1..10000</a>
%H A327790 Wikipedia, <a href="https://en.wikipedia.org/wiki/Multiplicative_group_of_integers_modulo_n">Multiplicative group of integers modulo n</a>
%e A327790 Let (Z/nZ)* be the multiplicative group of integers modulo n.
%e A327790 (Z/63Z)* = C_6 X C_6, so a(63) = phi(6)*phi(6) = 4.
%e A327790 (Z/513Z)* = C_18 X C_18, so a(513) = phi(18)*phi(18) = 36.
%e A327790 (Z/840Z)* = C_2 X C_2 X C_2 X C_2 X C_12, so a(840) = phi(2)^4*phi(12) = 4.
%o A327790 (PARI) a(n) = prod(i=1,#znstar(n)[2],eulerphi(znstar(n)[2][i]))
%Y A327790 Cf. A000010, A327791.
%K A327790 nonn
%O A327790 1,5
%A A327790 _Jianing Song_, Sep 25 2019