OFFSET
1,3
COMMENTS
Conjecture: ratio of non-sigma numbers tends to one. Increasing majority of numbers is impossible as a sum of divisors.
FORMULA
a(n) is the number of terms in A007369 not exceeding 2^n.
EXAMPLE
n=5: {2,5,9,10,11,16,17,19,21,22,23,25,26,27,29} are the 15 terms <= 2^5 in A007369.
MATHEMATICA
Table[{a={}; Do[s=DivisorSigma[1, n]; a=Append[a, s], {n, 1, 2^j}];
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer and Antti Karttunen, Jun 07 2004
EXTENSIONS
a(19)-a(31) from Donovan Johnson, Nov 30 2008
a(32)-a(33) from Donovan Johnson, Aug 06 2011
STATUS
approved