A067758 Numbers k such that sigma(prime(k) - 1) == 0 (mod k).

1, 4, 9, 27, 42, 60, 64, 70, 78, 144, 168, 180, 216, 238, 260, 318, 558, 600, 672, 960, 1008, 1053, 1260, 1620, 1806, 2112, 3318, 3780, 4608, 5544, 12152, 40084, 40095, 41664, 47040, 48825, 49176, 51870, 59832, 60528, 71040, 99008, 100356, 113904, 132000, 159000

Offset: 1

Author

Benoit Cloitre, Feb 05 2002

Keywords

• nonn

Comments

There are 91 terms up to and including 10 million. - Harvey P. Dale, Oct 04 2016

Links

• Amiram Eldar, Table of n, a(n) for n = 1..163 (terms 1..91 from Harvey P. Dale)

Crossrefs

Cf. A000203, A006093, A008332.

Programs

Mathematica

Select[Range[120000],Divisible[DivisorSigma[1,Prime[#]-1],#]&] (* Harvey P. Dale, Oct 04 2016 *)

PARI

for(k=1,120000, if(sigma(prime(k)-1)%k==0,print1(k,",")))

Extensions

More terms from Klaus Brockhaus, Feb 07 2002