Tunapotillion is equal to 103*103*101.2*1016+3*101,500+3. The term was coined by Trakaplex trying to make puns on Bowers' illions on answers.com.  This was the first confirmed quantity, though the name itself was first mentioned on a jocular Googology Testing wiki post trying to use illions as examples in sentences.
Approximations in other notations
It comes from 'tunillion' and 'potillion' with an "a" vowel first introduced in Tier 3.
- what is the biggest known number answers.com 1/14/2021.
- Onliyetapunillion? Gota-tenda-horsi-onli-yeta-palillion? Googology Testing Wiki. Nov 25, 2020.[dead link]