Quadruplet in a sentence as a noun

That's like saying UTF-8 requires "nonsense" pair, triplet, or quadruplet chars.

A triplet is just an atom plus a pair, and a quadruplet is an atom plus a triplet, and so forth.

Same is true for triples, quadruplets, ... with different probabilities.

Quadruplet definitions

noun

the cardinal number that is the sum of three and one

noun

one of four children born at the same time from the same pregnancy

See also: quad

noun

a set of four similar things considered as a unit

See also: quartet quartette quadruple