A078558 GCD of sigma(p#) and phi(p#) where p# = A002110(n) is the product of the first n primes.

1, 2, 8, 48, 96, 1152, 9216, 1658880, 3317760, 92897280, 2786918400, 100329062400, 802632499200, 370816214630400, 741632429260800, 2966529717043200, 29665297170432000, 355983566045184000

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..400

Formula

a(n) = gcd(A000203(A002110(n)), A000005(A002110(n))) = gcd(A005867(n), A054640(n)).

Example

m=2,3,30,210 primorials are balanced numbers so these GCD() equals phi(): a(n)=1,2,8,48 (see A005867).

Mathematica

GCD[DivisorSigma[1, #], EulerPhi[#]]&/@FoldList[Times, Prime[Range[20]]] (* Harvey P. Dale, Feb 28 2016 *)

Prog

(PARI) a(n)=gcd(prod(i=1, n, prime(i)-1), prod(i=1, n, prime(i)+1)) \\ Charles R Greathouse IV, Dec 09 2013

Crossrefs

Cf. A000203, A002110, A000005, A005867, A054640, A020492.

Sequence in context: A358822 A003275 A253665 * A003032 A193944 A058928

Adjacent sequences: A078555 A078556 A078557 * A078559 A078560 A078561

Keyword

nonn

Author

Labos Elemer, Dec 06 2002

Status

approved