2+4+8+16+32+64+……+1048576
=2+2+4+8+16+32+64+……+1048576-2
=4+4+8+16+32+64+……+1048576-2
=8+8+16+32+64+……+1048576-2
=……
=1048576+1048576-2
=2097152-2
=2097150
2+4+8+16+32+64+……+1048576
=2+2+4+8+16+32+64+……+1048576-2
=4+4+8+16+32+64+……+1048576-2
=8+8+16+32+64+……+1048576-2
=……
=1048576+1048576-2
=2097152-2
=2097150