Solved problem 31.
Integrated square root functin.
Solved problem 32.
Fixed calling function name and supported negative number.
Solved problem 33.
Solved problem 34.
Removed unnecessary map.
Solved problem 35.
Used  instead of '/' to make code concise.
Solved problem 36.
Used grop instead of groupBy.
Solved problem 37.
More concise with use of 'product'.
Solved problem 39.
Fixed a bug that small primes are not found.
Solved problem 40.
Fixed so that a pair of the same primes could be an answer.
Solved problem 41.
Added a condition that another prime should be bigger than specified number.
Added a link to problem 31-40.