"Forthtillion" doesn't appear in any of my reference works. If you mean quadrillion, that's 15 zeros. If you made it up, you can have as many zeros as you want.
fithtillion
how many zeros in one billion
Seven zeros.
33 zeros
there are 21 zeros
12 zeros.12 zeros.12 zeros.12 zeros.
Six zeros: 127,000,000
how many zeros in 12 lakh
9 zeros
10 zeros
11 zeros
101 zeros.