All possible combinations of a base58 (p2sh) address are 60^33 (= 47751966659678405306351616000000000000000000000000000000000)
Why 60^33? There are 64 characters (letters plus numbers), but bitcoin addresses don't have zeros (0), capital omikrons (O), l (small L) and I (capital of i) so they wouldn't confuse the people. A base58 (p2sh) address has 34 total characters, minus the first letter that it's always "3", we have 33 characters.
Thus, 60^33.
I'm not gonna tell you that brute forcing an address and actually succeeding is a miracle, because, hehe, you already knew it.
Although, I would like to show you what are the odds of succeeding with fewer characters, by taking a computer that makes 1M hashes per second.
This is the address I'm gonna focus:
3D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9r. Now let's remove the first letter, because it will always be the same:
D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9rThe first 3 letters of the address would take 120.000 hashes to make them, which is less than a second for the mentioned computer. Now, let the fun begin:
D2oe would take: 12 seconds (12960000 hashes)
D2oet would take: 13 minutes (777600000 hashes)
D2oetd would take: 13 hours (46656000000 hashes)
D2oetdN would take: 1 month (2799360000000 hashes)
D2oetdNu would take: 5.4 years (167961600000000 hashes)
D2oetdNuZ would take: 324 years (10077696000000000 hashes)
D2oetdNuZU would take: 19,440 years (604661760000000000 hashes)
D2oetdNuZUq would take: 1,166,400 years (36279705600000000000 hashes)
D2oetdNuZUqQ would take: 69,984,000 years (2176782336000000000000 hashes)
D2oetdNuZUqQH would take: 4,199,040,000 years (130606940160000000000000 hashes)
D2oetdNuZUqQHP would take: 251,942,400,000 years (7836416409600000000000000 hashes)
D2oetdNuZUqQHPJ would take: 15,116,544,000,000 years (470184984576000000000000000 hashes)
D2oetdNuZUqQHPJm would take: 906,992,640,000,000 years (28211099074560000000000000000 hashes)
D2oetdNuZUqQHPJmc would take: 54,419,558,400,000,000 years (1692665944473600000000000000000 hashes)
D2oetdNuZUqQHPJmcM would take: 3,265,173,504,000,000,000 years (101559956668416000000000000000000 hashes)
D2oetdNuZUqQHPJmcMD would take: 195,910,410,240,000,000,000 years (6093597400104960000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDD would take: 11,754,624,614,400,000,000,000 years (365615844006297600000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDH would take: 705,277,476,864,000,000,000,000 years (21936950640377856000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHY would take: 42,316,648,611,840,000,000,000,000 years (1316217038422671360000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHYo would take: 2,538,998,916,710,400,000,000,000,000 years (78973022305360281600000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHYoq would take: 152,339,935,002,624,000,000,000,000,000 years (4738381338321616896000000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHYoqk would take: 9,140,396,100,157,440,000,000,000,000,000 years (284302880299297013760000000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHYoqky would take: 548,423,766,009,446,400,000,000,000,000,000 years (17058172817957820825600000000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHYoqkyN would take: 32,905,425,960,566,784,000,000,000,000,000,000 years (1023490369077469249536000000000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHYoqkyNV would take: 1,974,325,557,634,007,040,000,000,000,000,000,000 years (61409422144648154972160000000000000000000000000000 hashes)
D2oetdNuZUqQHPJmcMDDHYoqkyNVs would take: 118,459,533,458,040,422,400,000,000,000,000,000,000 years
(3684565328678889298329600000000000000000000000000000 hashes)D2oetdNuZUqQHPJmcMDDHYoqkyNVsF would take: 7,107,572,007,482,425,344,000,000,000,000,000,000,000 years
(221073919720733357899776000000000000000000000000000000 hashes)D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk would take: 426,454,320,448,945,520,640,000,000,000,000,000,000,000 years
(13264435183244001473986560000000000000000000000000000000 hashes)D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9 would take: 25,587,259,226,936,731,238,400,000,000,000,000,000,000,000 years
(795866110994640088439193600000000000000000000000000000000 hashes)And finally, the entire address would take: 1,535,235,553,616,203,874,304,000,000,000,000,000,000,000,000 years to be brute forced successfully, which is equal with: 47751966659678405306351616000000000000000000000000000000000 hashes.Technically, I think it would be easier to add 1000 new blocks to the blockchain within 3 seconds than succeeding on something that big.
Please correct me if I've made a big mistake. This post is a bit useless, because you already knew how hard is to guess/brute force an address, but I would like to show you how impossible it is with numbers.