The guy can't memorize times tables. That is not just random "memorization", there are patterns and other contextual clues such as relationships to prime numbers, etc.
I imagine he has difficulty learning new words, terms, acronyms, etc.
That level of memorization is absolutely a core requirement for education and understanding.
How can you understand complex concepts if you can't remember the simple ones?
Wrong. I can't memorize my times tables either. I am consistently above average in my math courses, and am now taking second year math courses. Think again. Understanding simple concepts and memorizing formulas/terms/tables are entirely different.
Dead? No excuse for laying off work.