Show Goldbach?s conjecture that every even integer greater than 2 is the sum of two primes is equivalent to the conjecture that every integer greater than 5 is the sum of three primes (Hint: If is n > 5, consider n ? 2 if n is even and n - 3 if n is odd, then use Goldbach; Conversely, if n > 2 is even, consider n + 2.) Solution Every even integer greater than 2 is the sum of two primes. Consider any integer >5. Let this number be l. Either l can be odd or l can be even. If l is odd, l-3 is even>2 and can be expressed as sum of two primes by the Goldbach. Thus l-3 = Sum of two primes Hence l = sum of two primes + 3 = sum of 3 primes --------------------------------------------------------------------------------- If l is even, l-2>2 Hence l-2 can be expressed as sum of two primes As a result l = 2+sum of 2 primes = sum of 3 primes. Tus proved.