21217028 has 12 divisors (see below), whose sum is σ = 42434112. Its totient is φ = 9093000.

The previous prime is 21217019. The next prime is 21217033. The reversal of 21217028 is 82071212.

21217028 is an admirable number.

It is a junction number, because it is equal to n+sod(n) for n = 21216994 and 21217012.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 378848 + ... + 378903.

It is an arithmetic number, because the mean of its divisors is an integer number (3536176).

Almost surely, 2^21217028 is an apocalyptic number.

21217028 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21217028 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21217028 is a wasteful number, since it uses less digits than its factorization.

21217028 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 757762 (or 757760 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 21217028 is about 4606.1945247677. The cubic root of 21217028 is about 276.8395809448.

The spelling of 21217028 in words is "twenty-one million, two hundred seventeen thousand, twenty-eight".