It was proposed by Christian Goldbach that every odd composite number
can be written as the sum of a prime and twice a square.

9 = 7 + 2*1(2)次方
15 = 7 + 2*22
21 = 3 + 2*32
25 = 7 + 2*32
27 = 19 + 2*22
33 = 31 + 2*12

It turns out that the conjecture was false.

What is the smallest odd composite that cannot be written as the sum of
a prime and twice a square?