21397949 has 2 divisors, whose sum is σ = 21397950. Its totient is φ = 21397948.

The previous prime is 21397931. The next prime is 21397997. The reversal of 21397949 is 94979312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20994724 + 403225 = 4582^2 + 635^2 .

It is a cyclic number.

It is not a de Polignac number, because 21397949 - 2⁸ = 21397693 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21397919) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10698974 + 10698975.

It is an arithmetic number, because the mean of its divisors is an integer number (10698975).

Almost surely, 2^21397949 is an apocalyptic number.

It is an amenable number.

21397949 is a deficient number, since it is larger than the sum of its proper divisors (1).

21397949 is an equidigital number, since it uses as much as digits as its factorization.

21397949 is an evil number, because the sum of its binary digits is even.

The product of its digits is 122472, while the sum is 44.

The square root of 21397949 is about 4625.7917160201. The cubic root of 21397949 is about 277.6242400150.

The spelling of 21397949 in words is "twenty-one million, three hundred ninety-seven thousand, nine hundred forty-nine".