21697937 has 2 divisors, whose sum is σ = 21697938. Its totient is φ = 21697936.

The previous prime is 21697927. The next prime is 21697939. The reversal of 21697937 is 73979612.

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., 15062161 + 6635776 = 3881^2 + 2576^2 .

It is a cyclic number.

It is not a de Polignac number, because 21697937 - 2⁸ = 21697681 is a prime.

Together with 21697939, 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 (21697939) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10848968 + 10848969.

It is an arithmetic number, because the mean of its divisors is an integer number (10848969).

Almost surely, 2^21697937 is an apocalyptic number.

It is an amenable number.

21697937 is a deficient number, since it is larger than the sum of its proper divisors (1).

21697937 is an equidigital number, since it uses as much as digits as its factorization.

21697937 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21697937 is about 4658.1044427964. The cubic root of 21697937 is about 278.9156059111.

The spelling of 21697937 in words is "twenty-one million, six hundred ninety-seven thousand, nine hundred thirty-seven".