Find the number of prime numbers less than 100 and whose square ends in 9.
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the unit digits of numbers whose squares and with 9 is 3,7
so the prime numbers should end with 3 and 7.
the numbers below hundred which end with 3 and 7 are
3 13 23 33 43 53 63 73 83 93 7 17 27 37 47 57 67 77 87 97
in this prime numbers are 3, 13, 23, 43, 53 ,73,83,7,17,37,47,67,97
the number of prime numbers are 13.
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