It appears that apple doesn't support this unless you are authenticated to apple on your android phone. This seems like a chicken egg situation or am I missing something. I don't always have my ipad handy when I'm working on my apple computer. But I do have my android phone handy. Is it asking too much for Apple to simply send a text message to my android phone with the 2-factor code?
iMac 21.5", macOS 10.14
Have you tried this?
Keep your trusted phone numbers up to date
To use two-factor authentication, you need at least one trusted phone number on file where you can receive verification codes. Consider verifying an additional trusted phone number other than your own phone number. If your iPhone is your only trusted device and it is missing or damaged, you will be unable to receive verification codes required to access your account.
You can update your trusted phone numbers when you follow these steps:
If you want to add a phone number, click Add a Trusted Phone Number and enter the phone number. Choose to verify the number with a text message or automated phone call, and click Continue. To remove a trusted phone number, click 
next to the phone number you want to remove.
Apple ID -Two-factor authentication
Have you tried this?
Keep your trusted phone numbers up to date
To use two-factor authentication, you need at least one trusted phone number on file where you can receive verification codes. Consider verifying an additional trusted phone number other than your own phone number. If your iPhone is your only trusted device and it is missing or damaged, you will be unable to receive verification codes required to access your account.
You can update your trusted phone numbers when you follow these steps:
If you want to add a phone number, click Add a Trusted Phone Number and enter the phone number. Choose to verify the number with a text message or automated phone call, and click Continue. To remove a trusted phone number, click next to the phone number you want to remove.
Apple ID -Two-factor authentication
But I do have my android phone handy. Is it asking too much for Apple to simply send a text message to my android phone with the 2-factor code?
This is a standard part of 2FA.
As Eric notes, a trusted PHONE NUMBER can be a landline or a non-Apple device.
2-factor authentication using code sent to android phone
