a for ackermann b for busy beaver c for centillion d for decker e for exponential f for FGH g for graham h for hardy i for illion j for jounce k for kilo l for loader m for moser n for numbers o for ordinals p for psi q for quantum r for rayo s for supercompact t for time u for uncomputable v for variable w for woodin x for xeno y for yes z for zetta.