21251816 has 16 divisors (see below), whose sum is σ = 41580000. Its totient is φ = 10163824.

The previous prime is 21251803. The next prime is 21251821. The reversal of 21251816 is 61815212.

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, 57566 + ... + 57933.

It is an arithmetic number, because the mean of its divisors is an integer number (2598750).

Almost surely, 2^21251816 is an apocalyptic number.

It is an amenable number.

21251816 is a deficient number, since it is larger than the sum of its proper divisors (20328184).

21251816 is a wasteful number, since it uses less digits than its factorization.

21251816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115528 (or 115524 counting only the distinct ones).

The product of its digits is 960, while the sum is 26.

The square root of 21251816 is about 4609.9691972941. The cubic root of 21251816 is about 276.9908028243.

The spelling of 21251816 in words is "twenty-one million, two hundred fifty-one thousand, eight hundred sixteen".