21006397 has 2 divisors, whose sum is σ = 21006398. Its totient is φ = 21006396.

The previous prime is 21006379. The next prime is 21006413. The reversal of 21006397 is 79360012.

Together with previous prime (21006379) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17089956 + 3916441 = 4134^2 + 1979^2 .

It is a cyclic number.

It is not a de Polignac number, because 21006397 - 2¹⁹ = 20482109 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21001397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10503198 + 10503199.

It is an arithmetic number, because the mean of its divisors is an integer number (10503199).

Almost surely, 2^21006397 is an apocalyptic number.

It is an amenable number.

21006397 is a deficient number, since it is larger than the sum of its proper divisors (1).

21006397 is an equidigital number, since it uses as much as digits as its factorization.

21006397 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2268, while the sum is 28.

The square root of 21006397 is about 4583.2736117321. The cubic root of 21006397 is about 275.9204288226.

The spelling of 21006397 in words is "twenty-one million, six thousand, three hundred ninety-seven".