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Note 4 - Warrants (Tables)

6 Months Ended

Jun. 30, 2021

Notes Tables

Schedule of Warrants or Rights, Assumptions Used [Table Text Block]

		*June 30, 2021*			*December 31, 2020*
Risk-free interest rate		0.1% to 0.7%			0.1% to 0.3%
Volatility		87.6% to 129.1%			113.7% to 127.4%
Expected life (years)		0.6 to 4.1			1.1 to 4.6
Dividend yield		—%			—%

Schedule of Warrant Activity [Table Text Block]

		*Number of Shares*				*Range of Warrant Exercise*								*Weighted Average*				*Weighted Average Remaining Contractual*
		*Under Warrant*				*Price per Share*								*Exercise Price*				*Life (Years)*
Balance at January 1, 2021			2,733,645			$	6.30			$	16.80			$	9.45				3.6
Granted			—				—				—				—				—
Exercised			(10,000	)			6.30				6.30				6.30				—
Expired			—				—				—				—				—
Balance at June 30, 2021			2,723,645			$	6.30			$	16.80			$	9.46				3.1
Exercisable at June 30, 2021			2,723,645			$	6.30			$	16.80			$	9.46				3.1