The subnet calculator

A /26 leaves 6 host bits, because 32 minus 26 is 6. The block is two to the power of 6, which is 64 addresses. The first address names the network and the last is the broadcast, so 62 remain for hosts. 64 is the block size rather than the host count, 30 belongs to a /27, and 126 belongs to a /25.

Moving from /24 to /26 adds two bits to the network part. Two extra bits give four combinations, so you get four /26 blocks of 64 addresses each, and they fill the original /24 exactly. The count comes from the difference in prefix length, not from the new prefix itself, and the original object is left unchanged.

A /31 has one host bit, so the block is two addresses. The usual rule would subtract the network and broadcast addresses and leave nothing, but RFC 3021 allows both addresses to be used on a point-to-point link, and Python returns both from hosts(). A /31 is valid for IPv4, and a /32 is the single-address case.

Each 255 sets eight bits, so the first three octets give 24 bits. The last octet, 192, is 128 plus 64, which is two more bits set. That makes 26 bits in all, so the prefix is /26. A /24 mask ends in 0, a /25 ends in 128, and a /27 ends in 224.