If you are talking longitude only and not latitude, and fewest total, think great circle routing:
SEA-LHR Delta 36
Depart 9:14pm arrive 3:05pm
LHR-ICN Korean Air 908
Depart 7:35pm Arrive 2:25pm
ICN-SEA Korean Air 19
Depart 6:20pm Arrive 12:35pm
Total transit time- approx- 39.5 hours
Rough air miles- 15470