docs.s4d.ch: Hints Subnet Mask Information

Number of Addresses	Number of Bits	Prefix	Classful Notation	Mask	Hex Mask
1	0	/32		255.255.255.255	ffffffff
2	1	/31		255.255.255.254	fffffffe
4	2	/30		255.255.255.252	fffffffc
8	3	/29		255.255.255.248	fffffff8
16	4	/28		255.255.255.240	fffffff0
32	5	/27		255.255.255.224	ffffffe0
64	6	/26		255.255.255.192	ffffffc0
128	7	/25		255.255.255.128	ffffff80
256	8	/24	1 C	255.255.255	ffffff00
512	9	/23	2 C	255.255.254	fffffe00
1 K	10	/22	4 C	255.255.252	fffffc00
2 K	11	/21	8 C	255.255.248	fffff800
4 K	12	/20	16 C	255.255.240	fffff000
8 K	13	/19	32 C	255.255.224	ffffe000
16 K	14	/18	64 C	255.255.192	ffffc000
32 K	15	/17	128 C	255.255.128	ffff8000
64 K	16	/16	1 B	255.255	ffff0000
128 K	17	/15	2 B	255.254	fffe0000
256 K	18	/14	4 B	255.252	fffc0000
512 K	19	/13	8 B	255.248	fff80000
1 M	20	/12	16 B	255.240	fff00000
2 M	21	/11	32 B	255.224	ffe00000
4 M	22	/10	64 B	255.192	ffc00000
8 M	23	/9	128 B	255.128	ff800000
16 M	24	/8	1 A	255	ff000000
32 M	25	/7	2 A	254	fe000000
64 M	26	/6	4 A	252	fc000000
128 M	27	/5	8 A	248	f8000000
256 M	28	/4	16 A	240	f0000000
512 M	29	/3	32 A	224	e0000000
1024 M	30	/2	64 A	192	c0000000