21568331 has 2 divisors, whose sum is σ = 21568332. Its totient is φ = 21568330.

The previous prime is 21568307. The next prime is 21568333. The reversal of 21568331 is 13386512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21568331 is a prime.

It is a super-2 number, since 2×21568331² = 930385804251122, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 21568333, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21568294 and 21568303.

It is not a weakly prime, because it can be changed into another prime (21568333) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10784165 + 10784166.

It is an arithmetic number, because the mean of its divisors is an integer number (10784166).

Almost surely, 2^21568331 is an apocalyptic number.

21568331 is a deficient number, since it is larger than the sum of its proper divisors (1).

21568331 is an equidigital number, since it uses as much as digits as its factorization.

21568331 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 29.

The square root of 21568331 is about 4644.1717237846. The cubic root of 21568331 is about 278.3591574479.

The spelling of 21568331 in words is "twenty-one million, five hundred sixty-eight thousand, three hundred thirty-one".