What was the number of the block in which SegWit got activated? And first transaction? It was definitely on August 24th 2017, but not sure about the block number. Many sources reference block 481,822; but others state 481,824.

Also, even if this was the first block to allow segwit transactions, what was the first very block that contained one of them?
This is a very old question but probably someone else needs to know the same:

SegWit was activated in block 481824 and that block has two p2wpkh txs:

dfcec48bb8491856c353306ab5febeb7e99e4d783eedf3de98f3ee0812b92bad in block 0000000000000000001c8018d9cb3b742ef25114f27563e3fc4a1902167f9893
f91d0a8a78462bc59398f2c5d7a84fcff491c26ba54c4833478b202796c8aafd in block 0000000000000000001c8018d9cb3b742ef25114f27563e3fc4a1902167f9893


I have to run my script against testnet in order to find the best p2wpk tx.