Plz help me .

This Can be done by counting

for n =1,10n+1 = 11    ..............prime number

for n = 3,10n+1 = 31 ................prime number

for  n = 4, 10n+1 = 41 ..............prime number

for n = 6, 10n+1 = 61 .................      "

for n = 7,10n+1 = 71 ................        "

so ther are five prime number as for n = 2,5,8,9 10n+1 will be equal to 21,51,81,91 respectively which are not prime numbers.