

A095380


Number of integers not exceeding 2^n that are impossible as sumofdivisors of other numbers.


0



1, 1, 2, 6, 15, 34, 75, 162, 337, 706, 1466, 2995, 6119, 12450, 25248, 51158, 103450, 209010, 421681, 850322, 1712673, 3447970, 6937759, 13952296, 28049834, 56369395, 113241087, 227428919, 456641954, 916642515, 1839651364, 3691364919, 7405635242
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OFFSET

1,3


COMMENTS

Conjecture: ratio of nonsigma numbers tends to one. Increasing majority of numbers is impossible as a sum of divisors.


LINKS

Table of n, a(n) for n=1..33.


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

Cf. A007369.
Sequence in context: A192980 A281970 A221719 * A287012 A336957 A073838
Adjacent sequences: A095377 A095378 A095379 * A095381 A095382 A095383


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



