<P> While listening, users are offered the ability to buy the songs or albums at various online retailers . More than 450 musical attributes are considered when selecting the next song . These 450 attributes are combined into larger groups called focus traits . There are 2,000 focus traits . Examples of these are rhythm syncopation, key tonality, vocal harmonies and displayed instrumental proficiency . </P> <P> The service has two subscription plans: a free subscription supported by advertisements, and a fee - based subscription without advertisements . There are advertisements in Pandora Mobile for mobile phones and in the Pandora computer appliance . In October 2014, less than 5 percent of active listeners were paying subscribers . At the time of Pandora's IPO in 2011, Pandora had 800,000 tracks from 80,000 artists in its library and 80 million users . By November 2014, Pandora had approximately doubled its library size, topping 1.5 million songs . As of October 2016, Pandora had 77.9 million active users . </P> <P> In September 2016, Pandora announced additional features and subscription options, including a mid-level subscription service known as Pandora Plus that offers advertisement - free streaming, offline playback support using a prediction mechanism and more skips and replays . Users of the free advertisements - included service also were provided more skips and replays in exchange for watching an advertisement . Pandora also announced the launch of an on - demand service similar to competitors such as Apple Music and Spotify . </P> <P> On March 13, 2017, Pandora launched Pandora Premium, a new service allowing users to listen to and create playlists of individual songs on demand . Pandora's suggestions engine suggests and recommends songs and albums, as well as generate playlists based on similar songs . Pandora also emphasized a use of machine learning and manual curation, and that it had filtered "karaoke tracks, knock - off covers and pet sounds (but not Pet Sounds) that slow down other other services" from its library . </P>

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