A058250 GCD of n-th primorial number and its totient.

1, 1, 2, 2, 6, 30, 30, 30, 30, 330, 2310, 2310, 2310, 2310, 2310, 53130, 690690, 20030010, 20030010, 20030010, 20030010, 20030010, 20030010, 821230410, 821230410, 821230410, 821230410, 13960916970, 739928599410, 739928599410

Offset

0,3

Links

Michael De Vlieger, Table of n, a(n) for n = 0..1000

Formula

a(n) = gcd(A002110(n), A000010(A002110(n)) = gcd(A002110(n), A005867(n)).

a(n) = A005867(n) / A038110(n+1). For example: For n = 4: a(4) = 48 / 8 = 6. - Jamie Morken, Apr 12 2019

Example

a(6) = gcd(30030,5760) = 30.

Maple

[seq(igcd(product(ithprime(k), k=1..m), product(ithprime(k)-1, k=1..m)), m=1..50)];

Mathematica

GCD[#, EulerPhi[#]]&/@Rest[FoldList[Times, 1, Prime[Range[30]]]] (* Harvey P. Dale, Dec 19 2012 *)
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 *)

Prog

(PARI) a(n) = my(pr=prod(k=1, n, prime(k))); gcd(pr, eulerphi(pr)); \\ Michel Marcus, Apr 13 2019

Crossrefs

Cf. A002110, A000010, A005867, A038110.

Sequence in context: A004304 A326907 A270487 * A179929 A278258 A067644

Adjacent sequences: A058247 A058248 A058249 * A058251 A058252 A058253

Keyword

nonn,look

Author

Labos Elemer, Dec 05 2000

Extensions

a(0) = 1 inserted by Michael De Vlieger, Apr 13 2019

Status

approved