the sequence 7362514 represents the diatonic chords in a key [diatonic just means the natural chords that occur in a key....In the key of C, that would be C, d min, e min ,F, G, Amin, Bdim.
each consecutive step of the the scale gets a consecutive number...
The theory nerds will almost instantly note all those numbers in roman
numerals,,,so vii, iii, vi, ii, V, I, IV, with the lower case meaning
minor chords and uppercase are major....it's actually a great shorthand
way of spelling the chords without having to say "minor" , "major", etc

SOOOO....7362514 shows the steps/chords of the key with each consecutive
chord being a "FOURTH" higher - from vii to iii is a fourth (a perfect 4th, for that matter)....and etc - using up all the naturally occurring (diatonic)
chords in a key.