The last digit of a fourth power indecimal can only be 0, 1, 5, or 6.
Inhexadecimal the last nonzero digit of a fourth power is always 1.[1]
Every positive integer can be expressed as the sum of at most 19 fourth powers; every integer larger than 13792 can be expressed as the sum of at most 16 fourth powers (seeWaring's problem).
^An odd fourth power is the square of an odd square number. All odd squares are congruent to 1 modulo 8, and (8n+1)2 = 64n2 + 16n + 1 = 16(4n2 + 1) + 1, meaning that all fourth powers are congruent to 1 modulo 16. Even fourth powers (excluding zero) are equal to (2kn)4 = 16kn4 for some positive integer k and odd integer n, meaning that an even fourth power can be represented as an odd fourth power multiplied by a power of 16.
