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Note 6 - Stockholders' Equity, Stock Options and Warrants - Summary of Transactions for Stock Options and Warrants (Details) - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2021
Dec. 31, 2020
Warrant [Member]    
Number of Shares Outstanding (in shares) 7,353,376 2,171,610
Average Exercise Price Outstanding (in dollars per share) $ 3.76 $ 15.26
Number of Shares Issued (in shares) 12,955,822 8,097,468
Average Exercise Price Issued (in dollars per share) $ 1.65 $ 1.547
Number of Shares Forfeited (in shares) (128,710)
Average Exercise Price Forfeited (in dollars per share) $ 95.11
Number of Shares Exercised (in shares) (5,247,059) (2,786,992)
Average Exercise Price Exercised (in dollars per share) $ 0.86 $ 0.79
Number of Shares Outstanding (in shares) 15,062,139 7,353,376
Average Exercise Price Outstanding (in dollars per share) $ 2.96 $ 3.76
Share-based Payment Arrangement, Option [Member]    
Number of Shares Outstanding (in shares) 1,013,547 766,424
Average Exercise Price Outstanding (in dollars per share) $ 5.41 $ 11.34
Number of Shares Issued (in shares) 10,680 319,851
Average Exercise Price Issued (in dollars per share) $ 0.69 $ 1.03
Number of Shares Forfeited (in shares) (18,078) (72,728)
Average Exercise Price Forfeited (in dollars per share) $ 9.89 $ 10.58
Number of Shares Exercised (in shares)
Average Exercise Price Exercised (in dollars per share)
Average Exercise Price Exercised (in dollars per share)
Number of Shares Outstanding (in shares) 1,006,149 1,013,547
Average Exercise Price Outstanding (in dollars per share) $ 5.25 $ 5.41