1,2
28 is the second perfect number A000396(2) and 7 is the second Mersenne prime A000668(2). For the structure of this sequence and its representation in base 2, see A135652. - Omar E. Pol (info(AT)polprimos.com), Mar 03 2008
Index entries for sequences related to divisors of numbers
a(n) = A161713(n-1). [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jun 21 2009]
Cf. A000396, A000668, A135652.
Sequence in context: A094057 A119267 A144978 * A018660 A018692 A161713
Adjacent sequences: A018251 A018252 A018253 * A018255 A018256 A018257
nonn,fini,full,easy
N. J. A. Sloane (njas(AT)research.att.com).
