Welcome to the forums. You are in the correct section for your question.
You would need 38760 tickets to cover ALL of the possible combinations for 20 numbers in a 6/49 lottery. This would be called a full wheel.
I would suggest using an abreviated wheel for your 20 numbers such as the one found at: http://lottotutor.com/tips/20wheel.html
This partial wheel, requiring only 10 tickets, will give you pretty good coverage of your 20 numbers and guarantees at least one 3 number prize win if the 20 number pool contains 6 hits.
Betting all of the combinations is just too many tickets to fill out
All the Best of Lotto Luck to You!