21528631 has 2 divisors, whose sum is σ = 21528632. Its totient is φ = 21528630.

The previous prime is 21528629. The next prime is 21528673. The reversal of 21528631 is 13682512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21528631 - 2¹ = 21528629 is a prime.

It is a super-2 number, since 2×21528631² = 926963905468322, which contains 22 as substring.

Together with 21528629, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21528631.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21528131) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10764315 + 10764316.

It is an arithmetic number, because the mean of its divisors is an integer number (10764316).

Almost surely, 2^21528631 is an apocalyptic number.

21528631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21528631 is an equidigital number, since it uses as much as digits as its factorization.

21528631 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2880, while the sum is 28.

The square root of 21528631 is about 4639.8955807216. The cubic root of 21528631 is about 278.1882642096.

The spelling of 21528631 in words is "twenty-one million, five hundred twenty-eight thousand, six hundred thirty-one".