21630431 has 4 divisors (see below), whose sum is σ = 21660912. Its totient is φ = 21599952.

The previous prime is 21630421. The next prime is 21630439. The reversal of 21630431 is 13403612.

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

It is a cyclic number.

It is not a de Polignac number, because 21630431 - 2¹⁸ = 21368287 is a prime.

It is a super-2 number, since 2×21630431² = 935751090491522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21630439) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14150 + ... + 15603.

It is an arithmetic number, because the mean of its divisors is an integer number (5415228).

Almost surely, 2^21630431 is an apocalyptic number.

21630431 is a deficient number, since it is larger than the sum of its proper divisors (30481).

21630431 is an equidigital number, since it uses as much as digits as its factorization.

21630431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30480.

The product of its (nonzero) digits is 432, while the sum is 20.

The square root of 21630431 is about 4650.8527175132. The cubic root of 21630431 is about 278.6260540071.

The spelling of 21630431 in words is "twenty-one million, six hundred thirty thousand, four hundred thirty-one".