21628931 has 4 divisors (see below), whose sum is σ = 21741192. Its totient is φ = 21516672.

The previous prime is 21628907. The next prime is 21628939. The reversal of 21628931 is 13982612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21628931 is a prime.

It is a super-2 number, since 2×21628931² = 935621312405522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21628939) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 55841 + ... + 56226.

It is an arithmetic number, because the mean of its divisors is an integer number (5435298).

Almost surely, 2^21628931 is an apocalyptic number.

21628931 is a deficient number, since it is larger than the sum of its proper divisors (112261).

21628931 is a wasteful number, since it uses less digits than its factorization.

21628931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 112260.

The product of its digits is 5184, while the sum is 32.

The square root of 21628931 is about 4650.6914539668. The cubic root of 21628931 is about 278.6196132548.

The spelling of 21628931 in words is "twenty-one million, six hundred twenty-eight thousand, nine hundred thirty-one".