21657331 has 2 divisors, whose sum is σ = 21657332. Its totient is φ = 21657330.

The previous prime is 21657289. The next prime is 21657367. The reversal of 21657331 is 13375612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21657331 - 2⁹ = 21656819 is a prime.

It is a super-2 number, since 2×21657331² = 938079972087122, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21657331.

It is not a weakly prime, because it can be changed into another prime (21657431) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10828665 + 10828666.

It is an arithmetic number, because the mean of its divisors is an integer number (10828666).

Almost surely, 2^21657331 is an apocalyptic number.

21657331 is a deficient number, since it is larger than the sum of its proper divisors (1).

21657331 is an equidigital number, since it uses as much as digits as its factorization.

21657331 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3780, while the sum is 28.

The square root of 21657331 is about 4653.7437617471. The cubic root of 21657331 is about 278.7415076475.

The spelling of 21657331 in words is "twenty-one million, six hundred fifty-seven thousand, three hundred thirty-one".