The mass number is 81, that means the sum of protons and neutrons is 81. But neutrons are equal to 1.317 times protons ( since 31.7% more neutrons as compared to protons), therefore, 

n= neutrons

p= protons

81= n+p

p*[1+31.7/100]=n

(p*131.7)/100 = n

81 = 2.317p

p = 35

the nearest element to these neutrons and protons is Bromine(Br)