68 is the smallest composite number that becomes prime when turned upside down: 89.
68 is the largest even number that is expressible as the sum of two primes in two different ways: 7 + 61 = 68 and 31 + 37 = 68.
68 has a representation as a sum of two squares: 68 = 22 + 82.
2 comments:
Please check this .. 84 = 41+43; 71+13 is another even number expressible as sum of 2 primes!
94 = 83+11; 94 = 89+5
98 = 79+19; 98 = 67+31
I guess, therefore, 98 will be the largest even number to be expressed as sum of two primes. However,the numbers 84,94,98 are all expressible as sum of two primes in more than two ways. Hence,68 could be the largest even integer that could be expressed as the sum of two primes in ,EXACTLY 2 different ways.
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