printf "%3d %20d %s\n", $_, ( 1 << $_ )-1,  unpack 'h*', pack 'Q>', 
    Math::BigInt->new( ( 1 << $_ )-1 ) for 50 .. 60;;
 50     1125899906842623 0030ffffffffffff
 51     2251799813685247 0070ffffffffffff
 52     4503599627370495 00f0ffffffffffff
 53     9007199254740991 00f1ffffffffffff
 54    18014398509481983 0004000000000000
 55    36028797018963967 0008000000000000
 56    72057594037927935 1000000000000000
 57   144115188075855871 2000000000000000
 58   288230376151711743 4000000000000000
 59   576460752303423487 8000000000000000
 60  1152921504606846975 0100000000000000