That's the correct formula since the homestead development phase.
100000 is here a constant and according to How does the Ethereum Homestead difficulty adjustment algorithm work? :
+ int(2**((block.number // 100000) - 2))
refers to
The difficulty bomb part, which increases the difficulty exponentially every 100,000 blocks.
EDIT
It seems this formula is no longer correct since the EIP-2384 : https://eips.ethereum.org/EIPS/eip-2384.
It specifies the following :
For the purposes of calc_difficulty, simply replace the use of block.number, as used in the exponential ice age component, with the formula:
fake_block_number = max(0, block.number - 9_000_000) if block.number >= MUIR_GLACIER_FORK_BLKNUM else block.number
This will delay the ice age by 52 million seconds (approximately 611 days), so the chain would be back at 20 second block times around July 2021. It’s important to note this pushes the ice age 4,000,000 blocks from ~block 8,800,000 NOT from when this EIP is activated in a fork.
"When Istanbul was put in place, Ethereum developers apparently forgot to adjust the feature known as the 'difficulty bomb'. The developer's forgetfulness caused a significant mishap, creating 'an unplanned reduction' of twenty percent in inflation rate and security on the Ethereum network."
I just started learning about the internal workings of Ethereum. This is a little disturbing.
– Picard78 Sep 09 '20 at 06:20"Therefore, it should be included in a scheduled hardfork at a certain block number. It’s suggested to include this EIP shortly after the Istanbul fork."
Istanbul was released Dec 4, 2019. EIP-2384 was released before Istanbul on Nov 20, 2019. Based on the dates the Ethereum Developers didn't forget.
– Picard78 Sep 09 '20 at 06:43