21397697 has 2 divisors, whose sum is σ = 21397698. Its totient is φ = 21397696.

The previous prime is 21397693. The next prime is 21397699. The reversal of 21397697 is 79679312.

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., 20349121 + 1048576 = 4511^2 + 1024^2 .

It is a cyclic number.

It is not a de Polignac number, because 21397697 - 2² = 21397693 is a prime.

It is a super-2 number, since 2×21397697² = 915722873807618, which contains 22 as substring.

Together with 21397699, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21397693) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10698848 + 10698849.

It is an arithmetic number, because the mean of its divisors is an integer number (10698849).

Almost surely, 2^21397697 is an apocalyptic number.

It is an amenable number.

21397697 is a deficient number, since it is larger than the sum of its proper divisors (1).

21397697 is an equidigital number, since it uses as much as digits as its factorization.

21397697 is an evil number, because the sum of its binary digits is even.

The product of its digits is 142884, while the sum is 44.

The square root of 21397697 is about 4625.7644773594. The cubic root of 21397697 is about 277.6231501662.

The spelling of 21397697 in words is "twenty-one million, three hundred ninety-seven thousand, six hundred ninety-seven".