User blog comment:PsiCubed2/Psi's Ever-Growing Googolism (PEGG)/@comment-28606698-20170509151344/@comment-30754445-20170509154306

There's no I and no O.

"Next letter" goes directly from H to J (and from N to P).

So H10 becomes J4 and we continue from there.

Also, the post you've linked to doesn't give the definitions of the letters for non-integer arguments. For those definition, see here (for E-H), here (for J-N) and here (for P).