expert - a person with special knowledge or ability who performs skillfully

adder - a person who adds numbers

number cruncher - someone able to perform complex and lengthy calculations

actuary, statistician - someone versed in the collection and interpretation of numerical data (especially someone who uses statistics to calculate insurance premiums)

subtracter - a person who subtracts numbers

enchiridion, handbook, vade mecum - a concise reference book providing specific information about a subject or location