|
Search: id:A095380
|
|
|
| A095380 |
|
Number of integers not exceeding 2^n that are impossible as sum-of-divisors of other numbers. |
|
+0
1
|
|
| 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
(list; graph; listen)
|
|
|
OFFSET
|
1,3
|
|
|
COMMENT
|
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} is the
|
|
MATHEMATICA
|
Table[{a={}; Do[s=DivisorSigma[1, n]; a=Append[a, s], {n, 1, 2^j}];
|
|
CROSSREFS
|
Cf. A093532, A007369.
Sequence in context: A056520 A078406 A101352 this_sequence A073838 A014303 A076060
Adjacent sequences: A095377 A095378 A095379 this_sequence A095381 A095382 A095383
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Labos E. and Antti Karttunen (labos(AT)ana.sote.hu; his-firstname.his-surname(AT)iki.fi), Jun 07 2004
|
|
EXTENSIONS
|
a(19)-a(31) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Nov 30 2008
|
|
|
Search completed in 0.002 seconds
|
