|
Search: id:A111303
|
|
|
| A111303 |
|
Numbers n such that 2^tau(n) = n + 1 (where tau(n) = number of divisors of n). |
|
+0
1
|
| |
|
|
OFFSET
|
1,2
|
|
|
COMMENT
|
It is clear that n+1 must be a power of 2. Hence n=2^k-1 for some k. Found k=1, 2, 4, 6, 8, 16, 32. No other k<150. - T. D. Noe (noe(AT)sspectra.com), Nov 04 2005
|
|
FORMULA
|
Note that this is different from the sequence A019434(n)-2.
|
|
MATHEMATICA
|
Select[Range[10^6], 2^DivisorSigma[0, # ] == # + 1 &]
2^Select[Range[150], DivisorSigma[0, 2^#-1]==#&] - 1 (Noe)
|
|
CROSSREFS
|
Cf. A046801 (number of divisors of 2^n-1).
Sequence in context: A062211 A024036 A103454 this_sequence A118339 A083858 A080948
Adjacent sequences: A111300 A111301 A111302 this_sequence A111304 A111305 A111306
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Nov 02 2005
|
|
EXTENSIONS
|
One more term from T. D. Noe (noe(AT)sspectra.com), Nov 04 2005
|
|
|
Search completed in 0.002 seconds
|
