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Do you know why only Blockchain.info is recognizing this tx and how is someone able to do this kind of transaction that will never confirm? I already saw one of those "Bitcoin Doublers" using this kind of transaction only visible by the blockchain.info explorer but never got a answer on why is this possible.
If you use a transaction which uses an input which is considered as invalid by a node, your transaction won't be mined and hence, unconfirmed forever. All nodes reject double-spend transactions or transactions which use a double-spend transaction as input or a transaction which uses an unconfirmed input which has double-spend transaction as input and so forth. But for some reason, Blockchain.info don't do that. Blockchain.info's mempool configuration is different from other block explorers. Therefore, you will be able to see such transactions and also "unconfirmed" balances in Blockchain.info.
Mempool - A place where node store transactions which it consider as valid. You can configure it in different ways.
https://bitcoin.stackexchange.com/questions/46152/how-do-transactions-leave-the-memory-poolhttps://bitcointalk.org/index.php?topic=1939408.msg19284845#msg19284845.
P.S. Normally, nodes also reject dust transactions, though, afaik blockchain.info don't.
Edit: Like crairezx20 already mentioned, this thread is closed. So please create a new thread in Development & Technical Discussion board if you have more doubts.
To calculate transaction fee, I recommend
https://jochen-hoenicke.de/queue/#24h using as reference.