21877831 has 2 divisors, whose sum is σ = 21877832. Its totient is φ = 21877830.

The previous prime is 21877829. The next prime is 21877837. The reversal of 21877831 is 13877812.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21877831 - 2¹ = 21877829 is a prime.

It is a super-2 number, since 2×21877831² = 957278978529122, which contains 22 as substring.

Together with 21877829, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21877837) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10938915 + 10938916.

It is an arithmetic number, because the mean of its divisors is an integer number (10938916).

Almost surely, 2^21877831 is an apocalyptic number.

21877831 is a deficient number, since it is larger than the sum of its proper divisors (1).

21877831 is an equidigital number, since it uses as much as digits as its factorization.

21877831 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18816, while the sum is 37.

The square root of 21877831 is about 4677.3743703065. The cubic root of 21877831 is about 279.6842997938.

The spelling of 21877831 in words is "twenty-one million, eight hundred seventy-seven thousand, eight hundred thirty-one".