The number next to th_flags refers to the value of the TCP code bits field inside the TCP header of the out of state packet. The field is a 6 bit mask that allows interpretation of the fields in the header, the bits can be combined to find the value:

FIN 0x01
SYN 0x02
RST 0x04
PUSH 0x08
ACK 0x10
URG 0x20

For Example,

10 - ACK
11 - FIN+ACK
18 - PUSH+ACK