21018397 has 2 divisors, whose sum is σ = 21018398. Its totient is φ = 21018396.

The previous prime is 21018323. The next prime is 21018401. The reversal of 21018397 is 79381012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17799961 + 3218436 = 4219^2 + 1794^2 .

It is a cyclic number.

It is not a de Polignac number, because 21018397 - 2²³ = 12629789 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21018317) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10509198 + 10509199.

It is an arithmetic number, because the mean of its divisors is an integer number (10509199).

Almost surely, 2^21018397 is an apocalyptic number.

It is an amenable number.

21018397 is a deficient number, since it is larger than the sum of its proper divisors (1).

21018397 is an equidigital number, since it uses as much as digits as its factorization.

21018397 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 21018397 is about 4584.5825327940. The cubic root of 21018397 is about 275.9729590885.

The spelling of 21018397 in words is "twenty-one million, eighteen thousand, three hundred ninety-seven".