A Smith number is a composite number whose digit sum equals the sum of digit sums of its prime factors (counted with multiplicity).
For example, 22 = 2 × 11. Digit sum of 22 is 2 + 2 = 4. Digit sum of factors: 2 + (1 + 1) = 4. Match! So 22 is a Smith number.
Named by Albert Wilansky in 1982 after his brother-in-law Harold Smith, whose phone number 4937775 turned out to have this property: 4+9+3+7+7+7+5 = 42 = (3) + (5) + (6+5) + (6+4+5+8+3) where the factorization is 3·5·65·65837... actually 4937775 = 3 · 5² · 65837, and 4+9+3+7+7+7+5 = 42 vs 3+5+5+(6+5+8+3+7) = 42. Yes.