Thirteen is the only number that matters here.
Twenty-eight cards are stacked into seven rows, one card at the apex widening to seven along the base. An Ace counts one, a Jack eleven, a Queen twelve. Find two uncovered cards that add to thirteen and both leave the table. A King, worth thirteen on its own, simply walks away unaccompanied.
A card becomes uncovered only when the two cards overlapping it below have gone, so the shape dissolves upward from the base. Twenty-four cards remain in the stock for the moments when nothing on the table pairs, turned one at a time and sent round again whenever the pile runs dry.
The difficulty is not the addition. It is choosing between two legal pairs when only one of them opens the row above. Beginners clear whatever they see; the deals that come out are the ones where you looked at the row overhead first and asked which removal was actually useful.
Plays without a connection, remembers your times and best runs, undoes your last hundred moves, and reads in 33 languages.
Pyramid solitaire: match pairs adding to 13. Free card game, offline.