What is the origin of an account's initial sequence number

Question

According to the stellar docs

Sequence number

The current transaction sequence number of the account. This number starts equal to the ledger number at which the account was created

This does not appear to be true. Take, for example the following account:

https://horizon-testnet.stellar.org/accounts/GAH4Q7KMQAYQQHXS5763UNPG5ZSOLROEZZHC4Y45BU3HIVH6RW3TBYBD

It was created in ledger 697113, but its sequence number started at 2994077536616448.

Where did this sequence number come from?

Answer 1

The ledger is bit shifted (but I don't know the reason why). 697113 << 32 = 2994077536616448

This is from stellar-core source:

getStartingSequenceNumber(LedgerTxnHeader const& header)
{
    return static_cast<uint64_t>(header.current().ledgerSeq) << 32;
}