1～20的自然数中，奇数有(r,A9b8E9V个，偶数有*B(w(o0I,L6I)j'N4b1v8_+B'_个，质数有/F2G)f6q0w0e3H0C/O3@6H.B+c:?6z-w-f-U1T2F8K/W)s个，合数有4j;T.h.A-F)`5p1p(H个。'Y8d8I6r4a+Q8m;`