Although this numbering (e.g. isatin molecule) is always reproducible but why is this abstruse numbering followed in GaussView? Why atom-1 is given to fused carbon and nitrogen is given atom-15?
The numbering of atoms in Gaussview depends on the way you build your molecule and there is no logical pattern for the numbering of these former of your molecule.
I would suggest you tu use clearly better software to build input for Gaussian calculation like "Avogadro" which is easier and user-friendly and offers a non-denigrable force field to obtain a quite acceptable guess before QM calculation.
Furthermore, Avogadro allows the user to choose the numbers for atoms (even though Molden is surely better to reoganize them). Finally you could consider numbering your atoms directly from the *.xyz file.