2 syllables:
clumber, cumber, cumbre, f-number, humber, l-number, lumber, number, scumber, slumber, umber

3 syllables:
accumber, alumbre, back-number, box-number, call number, discumber, e-number, encumber, f number, incumber, kachumber, large number, mach number, macumber, mass number, mccumber, misnumber, outnumber, page number, phone number, prime number, real number, renumber, stop number, wave number, whole number

4 syllables:
antenumber, complex number, compound number, disencumber, dumb and dumber, dunbar's number, iliolumbar, index number, license number, magic number, not-a-number, octane number, paint-by-number, po box number, sacrolumbar, unencumber, wavenumber

5 syllables:
atomic number, cardinal number, natural number, opposite number, rational number, telephone number, thoracolumbar

6 syllables:
algebraic number, irrational number, registration number, transcendental number

7 syllables:
imaginary number

8 syllables:
basic reproduction number, identification number, pure imaginary number, social security number

9 syllables:
bank identification number, vat identification number

12 syllables:
imaginary part of a complex number

2 syllables:
blunder, bumper, bunker, bunter, dumper, dunker, hunger, hunter, jumper, junker, lumper, monger, plunder, plunker, punter, shunter, stumper, sunder, thunder, tunker, unbar, under, wonder, younger, younker

3 syllables:
editor, decolor, semaphore, sepulcher, nebular, hellebore, delaware, belshazzar, predator, headhunter, ecuador, creditor, metaphor, guenevere, specular, senator, messenger, settler, metamere, secretaire, escolar, leveller, debugger, elater, prelature, seminar, stepmother, sepulture, reckoner, megathere, reservoir, cellular, tetraspore, questioner, wrestler, seconder, sepulchre, pedaler, regular, medicare, megaspore, premolar, belabour, presenter, temperature, pensioner, reveler, stepbrother, stegosaur, secular, asunder, bob under, boy wonder, bug-hunter, fall under, fox hunter, go under, like thunder, pole jumper, pothunter, put under, ski jumper, spelunker, the hunter, tub-thumper, witch-hunter

4 syllables:
emmentaler, centromere, confectioner, noncellular, executor, dosemeter, irregular, expenditure, developer, molecular, acellular, misdemeanour, investiture, corregidor, text editor, room temperature, embezzler, competitor, ctenophore, buckle under, fortune hunter, going under, knuckle under, lion-hunter, newtown wonder, power hunger

5 syllables:
body temperature, intracellular, primogenitor, extracellular, curie temperature, city editor, copy editor, linkage editor, kentucky wonder, parachute jumper

6 syllables:
managing editor, differentiator, absolute temperature

7 syllables:
capital expenditure