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 A378056 #10 Nov 16 2024 02:56:26
%S A378056 1,1,2,3,2,2,2,3,4,6,2,30,2,6,4,15,2,20,2,6,4,6,2,210,6,6,4,6,2,84,2,
%T A378056 15,4,6,12,420,2,6,4,126,2,60,2,30,8,6,2,210,8,6,4,30,2,20,12,90,4,6,
%U A378056 2,4620,2,6,40,45,6,84,2,6,4,36,2,420,2,6,24,30,12
%N A378056 a(n) = gcd(A057643(n), A084190(n)) = gcd(lcm{d+1 : d|n}, lcm{d-1 : d > 1 and d|n}).
%H A378056 Amiram Eldar, <a href="/A378056/b378056.txt">Table of n, a(n) for n = 1..10000</a>
%F A378056 a(n) == 1 (mod 2) if and only if n is a power of 2 (A000079).
%F A378056 a(p) = 2 for an odd prime p. Composite numbers k such that a(k) = 2 are listed in A378057.
%t A378056 a[n_] := Module[{d = Divisors[n]}, GCD[LCM @@ (d + 1), LCM @@ (Rest @ d - 1)]]; a[1] = 1; Array[a, 100]
%o A378056 (PARI) a(n) = {my(d = divisors(n)); gcd(lcm(apply(x->x+1, d)), lcm(apply(x -> if(x > 1, x-1, x), d)));}
%Y A378056 Cf. A000079, A057643, A084190, A378053, A378057.
%K A378056 nonn
%O A378056 1,3
%A A378056 _Amiram Eldar_, Nov 15 2024