This is been an odd duck to me recently:
LGA-DEN-LGA
361 310
405 406
745 776
409 408
IIRC, back when I did this commute many years ago, I thought it was:
LGA-DEN-LGA
403 402
405 404
407 406
409 408
My memory could be wrong, but it made so much more sense back then. They did cut a few routes lately due to LGA time table issues, so it could have lead to the re-numbering I guess.