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Answer
Hi Utpal,
164 mod 98 = 66
So, 164^438 mod 98 = 66^438 mod 98
= (33 * 66^437 mod 49)*2
66 mod 49 = 17
= (33 * 17^437 mod 49)*2
17 and 49 are co-prime
Euler totient of 49 = 49*(1 - 1/7) = 42
So, 17^42 mod 49 = 1 => 17^420 mod 49 = 1
So, (33 * 17^17 mod 49) * 2
17^2 mod 49 = -5
= (33 * 17 * -5^8 mod 49)*2
= (33 * 17 * 37 * 37 mod 49)*2
= 32 * 2 = 64
