def get_pentagonal_number(n)
return n*(3*n-1)/2
end
Use the method to find the 10th pentagonal number
puts get_pentagonal_number(10)
main.rb
Here, we have used the formula for nth pentagonal number `n(3n-1)/2`. The formula is enclosed in a method called `get_pentagonal_number`. We passed `10` as an argument to our method to find the 10th pentagonal number. The output will be `145`.