The number of 401(k) accounts with balances of at least $1 million at Fidelity Investments grew 84% year over year to 412,000, while the number of seven-figure IRAs jumped more than 64% to 341,600, Fidelity said. Together, the number of accounts with $1 million or more grew 74.5% — though it isn’t clear how many individuals that represents, because people can have multiple accounts.