21397631 has 2 divisors, whose sum is σ = 21397632. Its totient is φ = 21397630.

The previous prime is 21397609. The next prime is 21397633. The reversal of 21397631 is 13679312.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21397631 - 2¹⁰ = 21396607 is a prime.

It is a super-2 number, since 2×21397631² = 915717224824322, which contains 22 as substring.

Together with 21397633, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21397633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10698815 + 10698816.

It is an arithmetic number, because the mean of its divisors is an integer number (10698816).

Almost surely, 2^21397631 is an apocalyptic number.

21397631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21397631 is an equidigital number, since it uses as much as digits as its factorization.

21397631 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6804, while the sum is 32.

The square root of 21397631 is about 4625.7573433979. The cubic root of 21397631 is about 277.6228647283.

The spelling of 21397631 in words is "twenty-one million, three hundred ninety-seven thousand, six hundred thirty-one".