A055681 Numbers k that divide sigma(k)-phi(k).

1, 2, 12, 42, 1242, 75960, 1447488, 3506976, 6137440, 10834488, 17156160, 90288000, 431440416, 454460160, 704592000, 1385119360, 1588268480, 10674673152, 24913095480, 31103703540, 56015374080, 80767843200, 129631788000, 463308768000, 469897798656, 834460413696

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Comments

a(37) > 10^13. - Giovanni Resta, Jun 12 2013

Links

• Giovanni Resta, Table of n, a(n) for n = 1..36 (terms < 10^13)

Crossrefs

Cf. A011774, A000203, A000010, A054024, A056075.

Programs

Maple

with(numtheory): A055681:=n->`if`(sigma(n)-phi(n) mod n=0,n,NULL): seq(A055681(n), n=1..10^5); # Wesley Ivan Hurt, Sep 13 2014

Mathematica

Do[If[Mod[DivisorSigma[1, n]-EulerPhi[n], n]==0, Print[n]], {n, 1, 10^9}]

PARI

for(n=1,10^8,if((sigma(n)-eulerphi(n))%n==0,print1(n,", "))) \\ Derek Orr, Sep 13 2014

Extensions

a(16)-a(26) from Donovan Johnson, Feb 28 2012