puzzle #39:
cuBitCrack.exe --keyspace 4000000000:7fffffffff 1EeAxcprB2PpCnr34VfZdFrkUWuxyiNE
          
Will scan search for a private key between 2 numbers:

 274 877 906 944
 549 755 813 887

Without the -r parameter the scan is performed linary like a counter  274 877 906 944,  274 877 906 945...

The solution key is

323 724 968 937

Bitcrack will check 48 847 061 993 seeds
with -r Bitcrack will faster if the private key is above  (549 755 813 887- 274 877 906 944)/2