398 = 2 x 199.
398 is the number of integers with integer complexity 22.
398 is the solution to the postage problem with two denominations and 37 stamps (A014616).
398 is a number n such that n10 + n9 + n8 + n7 + n6 + n5 + n4 + n3 + n2 + n + 1 is prime (A162862).
398 is the smallest even number with digit sum 20 (A069532).
398 and the 398th prime (2729) have only the digit 9 in common (A107940).
Source: What's Special About This Number?