A=1+21+22+23+...+210
2A=21+22+23+24+...+211
2A-A=21+22+23+24+...+211-(1+21+22+23+...+210)
A=211-1
A= 2048-1
A= 2047
A = 20 + 21 + 22 + ... + 210
2A = 21 + 22 + 23 + ... + 211
2A - A = (21 + 22 + 23 + ... + 211) - (20 + 21 + 22 + ... + 210)
A = 211 - 20
A = 2048 - 1 = 2047
A=1+21+22+23+..+210
=> A=20+21+22+23+..+210
A = 1 + 2 + 22 + 23 + ......... + 210
=> 2A = 2 + 22 + 23 + ......... + 211
=> 2A - A = 211 - 1
=> A = 211 - 1
