21698387 has 2 divisors, whose sum is σ = 21698388. Its totient is φ = 21698386.

The previous prime is 21698321. The next prime is 21698401. The reversal of 21698387 is 78389612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21698387 - 2¹⁸ = 21436243 is a prime.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21692387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10849193 + 10849194.

It is an arithmetic number, because the mean of its divisors is an integer number (10849194).

Almost surely, 2^21698387 is an apocalyptic number.

21698387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21698387 is an equidigital number, since it uses as much as digits as its factorization.

21698387 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 145152, while the sum is 44.

The square root of 21698387 is about 4658.1527454561. The cubic root of 21698387 is about 278.9175340692.

The spelling of 21698387 in words is "twenty-one million, six hundred ninety-eight thousand, three hundred eighty-seven".