OFFSET
1,1
COMMENTS
sigma(sigma(A046528(2,12,13,18,21,22,56,57,175,176,177,..))) is Mersenne prime.
FORMULA
EXAMPLE
45091651584=2^18*3*7*8191, sigma(45091651584)=137438691328 is perfect number.
CROSSREFS
KEYWORD
nonn
AUTHOR
Manuel Valdivia, Oct 12 2010
STATUS
approved