• Back in recur(32)
• Finished the recursive call, got back "101"
• Computes "2" + "101", which is "2101"
• Stops and returns "2101"

Resulting call stack

r(1)  returns "1"
r(3)     dig -> "0"    "0" + "1"   returns "01"
r(10)    dig -> "1"    "1" + "01"  returns "101
r(32)    dig -> "2"    "2" + "101" returns "2101"

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