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A095380 Number of integers not exceeding 2^n that are impossible as sum-of-divisors 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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Conjecture: ratio of non-sigma 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

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Last modified September 19 07:24 EDT 2020. Contains 337178 sequences. (Running on oeis4.)