Riot Blockchain, a Bitcoin mining company, has seen several developments lately. There was an update regarding its March production numbers as well as an operations update. Its stock has been rising due to some of these developments. What is Riot's stock forecast for 2021? Is the stock a buy or a sell?Riot Blockchain uses sophisticated machines and software to mine Bitcoin. Its share price is largely dependent on the changes in Bitcoin's price.Why Riot Blockchain stock is risingRIOT stock has risen by nearly 250 percent YTD. The stock surged by 15 percent on April 13 alone. There are several reasons why Riot Blockchain stock has been rising. One is the strong gains in Bitcoin. On April 13, Bitcoin hit an all-time high and surpassed $63,000 for the first time ever. This implies gains of more than 800 percent for Bitcoin YoY.The company released its March production numbers as well as operations updates on April 12. In March, Riot Blockchain produced 187 Bitcoin—an increase of 80 percent over its pre-halving March 2020 production numbers. This strong update also supported the stock price.Coinbase is set to IPO on Nasdaq on April 14. Investors’ excitement about this IPO benefits crypto mining companies, including RIOT and Marathon Digital.Forecast for RIOT stockRiot Blockchain stock is just covered by one Wall Street analyst, HC Wainwright, according to Market Beat. The analyst has a buy rating on the stock with a target price of $64. The target price implies a potential upside of 8 percent for the stock.Recently, Citron Research tweeted and said that RIOT stock should be trading at $2, in line with its NAV (net asset value). The stock is currently trading closer to $60.Is RIOT stock overvalued?Citron’s tweet has ignited a debate about whether Riot stock is overvalued. Citron mentioned that if investors want exposure to Bitcoin, it's better to buy Bitcoin itself or Grayscale Bitcoin Trust, which is an investment vehicle that provides exposure to Bitcoin. If RIOT were to trade based on the Bitcoins it has and the value of its plant, property, and equipment, its stock price should be closer to $2.Citron made this point regarding valuing RIOT based on its NAV because RIOT isn't selling many Bitcoins to be funding its business through operations. In fact, it's holding most of the Bitcoins mined. However, there's one key point of differentiation while valuing a company based on its NAV alone. The company shouldn't be doing anything to grow its business or expanding in any way. However, that isn't the case with RIOT. The company has been increasing its mining capabilities, which should ideally lead to an accelerated mining pace. RIOT’s stock price shouldn't be trading at $2 or near this level.Most of the gains in the stock price are due to gains in Bitcoin's price. Due to a leveraged play on Bitcoin, after a point, every dollar rise in Bitcoin's price will flow directly to RIOT’s bottom-line. Investors are factoring in this leveraged nature of the company to bid the stock up, which is fairly reasonable.Will RIOT stock rise more?Investors didn’t pay much attention to Citron’s argument. The stock traded up by about 15 percent on the same day the research firm tweeted its argument against RIOT. So far, Bitcoin and cryptocurrency mining names are seeing positive momentum in 2021. Many high-profile people like Tesla CEO Elon Musk and billionaire investor Chamath Palihapitiya are favoring and propagating Bitcoin. This has also generated positive interest for the cryptocurrency.Going forward, the positive momentum in Bitcoin should continue as people look for ways to diversify away from government and central banks’ controlled currencies. The decentralized nature of Bitcoin has been one of its winning traits lately. It's expected to continue to gain widespread acceptance, which would lead to gains in its price. This should be positive for crypto mining stocks, including RIOT.