Question: what are rare dollar bills?
Answer: Seven repeating digits in a row on $1 bills (i.e., 18888888, 59999999)
Seven of the same number on $1 bills (i.e., 99909999, 00010000)
Super repeaters on $1 bills (i.e., 67676767)
Double quads on $1 bills (i.e., 44440000)
Super radars on $1 bills (ie: 01111110, 80000008)