21315797 has 2 divisors, whose sum is σ = 21315798. Its totient is φ = 21315796.

The previous prime is 21315793. The next prime is 21315799. The reversal of 21315797 is 79751312.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20557156 + 758641 = 4534^2 + 871^2 .

It is a cyclic number.

It is not a de Polignac number, because 21315797 - 2² = 21315793 is a prime.

Together with 21315799, 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 (21315793) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10657898 + 10657899.

It is an arithmetic number, because the mean of its divisors is an integer number (10657899).

Almost surely, 2^21315797 is an apocalyptic number.

It is an amenable number.

21315797 is a deficient number, since it is larger than the sum of its proper divisors (1).

21315797 is an equidigital number, since it uses as much as digits as its factorization.

21315797 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13230, while the sum is 35.

The square root of 21315797 is about 4616.9033994659. The cubic root of 21315797 is about 277.2684950679.

The spelling of 21315797 in words is "twenty-one million, three hundred fifteen thousand, seven hundred ninety-seven".