the number that is represented as a one followed by 24 zeros
<noun.quantity> in England they call a septillion a quadrillion
the number that is represented as a one followed by 15 zeros
<noun.quantity>
Quadrillion \Quad*ril"lion\, n. [F., fr. L. quater four times, akin to quattuor four, E. four; -- formed like million. See {Four}, {Million}.] According to the French notation, which is followed also upon the Continent and in the United States, a unit with fifteen ciphers annexed; according to the English notation, the number produced by involving a million to the fourth power, or the number represented by a unit with twenty-four ciphers annexed. See the Note under {Numeration}.