Keep practising…
Think you’re good at maths? Or know someone who is? Then you or they won’t want to read about Gert Mittring, who can calculate the 13th root of hundred digit numbers in less than 12 seconds. (The “13th” root means what number multiplied together with itself 13 times gives the original number. E.g., the 3rd root (also called cube root) of 27 is 3, since 3×3x3=27.) He can also memorise 22 random digits in four seconds!
Of course, to what extent this ability translates into “practical” mathematics isn’t clear - he’s clearly intelligent (from the degrees he’s completed), but there are many different types of brilliance.