The number is "fifteen thousand four hundred nine".
In addition to my normal speech, I can say it in maybe ten different regional dialects and foreign accents, but none of them really well. I can also say it in four foreign languages that are not English.
You can "say" 15409 in potentially infinite ways: 15,000 + 409 15,001 + 408 15,002 + 407 etc.
To write 15,409 in expanded form, just take each digit and write the following ones as zeroes, adding them together like so: 10,000 + 5,000 + 400 + 9 We leave out the "00" because that doesn't have any real value.
