My guess is 65. I don't know what sequence the first, third numbers are but observing the others it is going 61...63.....65....67
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9
46. It's the square numbers with their digits reversed: 9 → 9 = 32 61 → 16 = 42 52 → 25 = 52 63 → 36 = 62 94 → 49 = 72 ??? 18 → 81 = 92 The missing number is the square of 8 with its digits reversed: 82 = 64 → 46.
Only 63 is a composite. 63 = 3 x 3 x 7 The other three numbers (13, 31, 61) are all prime numbers.
The numbers are 57, 59, 61 and 63.
The numbers are 57, 59, 61 and 63.