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%I #36 Apr 26 2019 02:57:20
%S 1,1,2,2,6,30,30,30,30,330,2310,2310,2310,2310,2310,53130,690690,
%T 20030010,20030010,20030010,20030010,20030010,20030010,821230410,
%U 821230410,821230410,821230410,13960916970,739928599410,739928599410
%N GCD of n-th primorial number and its totient.
%H Michael De Vlieger, <a href="/A058250/b058250.txt">Table of n, a(n) for n = 0..1000</a>
%F a(n) = gcd(A002110(n), A000010(A002110(n)) = gcd(A002110(n), A005867(n)).
%F a(n) = A005867(n) / A038110(n+1). For example: For n = 4: a(4) = 48 / 8 = 6. - _Jamie Morken_, Apr 12 2019
%e a(6) = gcd(30030,5760) = 30.
%p [seq(igcd(product(ithprime(k), k=1..m), product(ithprime(k)-1, k=1..m)), m=1..50)];
%t GCD[#,EulerPhi[#]]&/@Rest[FoldList[Times,1,Prime[Range[30]]]] (* _Harvey P. Dale_, Dec 19 2012 *)
%t Fold[Append[#1, {#1, #2, GCD[#1, #2]} & @@ {#4 #1, #2 (#4 - 1)} & @@ Append[#1[[-1]], #2]] &, {{1, 1, 1}}, Prime@ Range[29]][[All, -1]] (* _Michael De Vlieger_, Apr 25 2019 *)
%o (PARI) a(n) = my(pr=prod(k=1, n, prime(k))); gcd(pr, eulerphi(pr)); \\ _Michel Marcus_, Apr 13 2019
%Y Cf. A002110, A000010, A005867, A038110.
%K nonn,look
%O 0,3
%A _Labos Elemer_, Dec 05 2000
%E a(0) = 1 inserted by _Michael De Vlieger_, Apr 13 2019
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