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Note 7 - Stockholders' Equity and Common Stock Warrants (Tables)
3 Months Ended
Mar. 31, 2022
Notes Tables  
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]
  

Outstanding

  

Range of exercise

price per share

  

Expiration dates

Common stock warrants issued related to the January 2018 common stock offering

  23,639  

$599.71

-$749.76  

January 2023

Common stock warrants issued related to the May 2019 common stock offering

  27,648  

$250.09

-$306.04  

May and December 2024

Common stock warrants issued related to the November 2019 common stock offering

  4,269   $17.51   

May 2024

Common stock warrants issued related to the December 2019 common stock offering

  6,264  

$21.68

-$34.92  

December 2024 and June 2025

Common stock warrants issued related to the May 2020 common stock offering

  11,424   $65.65   

March 2025

Common stock warrants issued related to the May 2020 investor warrant exercise

  4,998   $29.7   

November 2025

Common stock warrants issued related to the February 2021 common stock offering

  33,649   $64.08   

February 2026

   111,891