Lower        Known        Upper
              bound        term   		bound
            
  a(1)                       1                    
  a(2)                       2                    
  a(3)                       4                    
  a(4)                       5                    
  a(5)                       8                    
  a(6)                      16                    
  a(7)                      28                    
  a(8)                      37                    
  a(9)                      64                    
 a(10)              112    ...             128    
 a(11)              185    ...             232   [1] 
 a(12)                     299
 a(13)              448    ...             512    
 a(14)              784    ...            1024    
 a(15)             1196    ...            1941    
 a(16)             2048    ...            2517   [2] 
 a(17)             3136    ...            4096    
 a(18)             5180    ...            8192    
 a(19)             8372    ...           16384    
 a(20)            12544    ...           21700    
 a(21)            21952    ...           32768    
 a(22)            34225    ...           65536    
 a(23)            57344    ...          131072    
 a(24)            89401    ...          190051    
 a(25)           145040    ...          262144    
 a(26)           234416    ...          524288    
 a(27)           378880    ...         1048576    
 a(28)           614656    ...         1683218    
 a(29)           958300    ...         2182396    
 a(30)          1605632    ...         4194304    
 a(31)          2503228    ...         8388608    
 a(32)          4194304    ...        15033173    
 a(33)         16777216    ...        19548046   [2]    
 a(34)         16777216    ...        33554432    
 a(35)         33554432    ...        67108864    
 a(36)         67108864    ...       134217728    
 a(37)         83886080    ...       176142312    
 a(38)        134217728    ...       268435456    
 a(39)        268435456    ...       536870912    
 a(40)        469762048    ...      1073741824    
 a(41)        620756992    ...      1594831736    
 a(42)       1073741824    ...      2147483648    
 a(43)       1879048192    ...      4294967296    
 a(44)       3103784960    ...      8589934592    
 a(45)       5016387584    ...     14497410186    
 a(46)       7516192768    ...     18844224462    
 a(47)      13153337344    ...     34359738368    
 a(48)      20065550336    ...     68719476736    
 a(49)      34359738368    ...    132224930146    
 a(50)      52613349376    ...    172186125456    

[1] Lower bound established by computer search - Bert Dobbelaere, Feb 14 2017
[2] Lower bound from YAAKOBI et al. "CODES FOR WRITE-ONCE MEMORIES" - 
    IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 58, NO. 9, SEPTEMBER 2012