A063785 Numbers n such that sigma(n) = 2n + omega(n), where omega(n) is the number of distinct prime divisors of n.

20, 104, 464, 1952, 4030, 5830, 130304, 522752, 1848964, 8382464, 134193152

Offset

1,1

Comments

It is easily proved that if 2^m-3 is prime then 2^(m-1)*(2^m-3) is in the sequence. - Farideh Firoozbakht, Feb 12 2008

Links

Table of n, a(n) for n=1..11.

Prog

(PARI) for(n=1, 10^8, if(sigma(n)==2*n+omega(n), print(n)))

Crossrefs

Cf. A045768.

Sequence in context: A189950 A045768 A088831 * A181703 A334419 A187756

Adjacent sequences: A063782 A063783 A063784 * A063786 A063787 A063788

Keyword

nonn,more

Author

Jason Earls, Aug 17 2001

Status

approved