21690407 has 2 divisors, whose sum is σ = 21690408. Its totient is φ = 21690406.

The previous prime is 21690397. The next prime is 21690413. The reversal of 21690407 is 70409612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21690407 - 2⁴ = 21690391 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21690407.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21690467) 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, 10845203 + 10845204.

It is an arithmetic number, because the mean of its divisors is an integer number (10845204).

Almost surely, 2^21690407 is an apocalyptic number.

21690407 is a deficient number, since it is larger than the sum of its proper divisors (1).

21690407 is an equidigital number, since it uses as much as digits as its factorization.

21690407 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3024, while the sum is 29.

The square root of 21690407 is about 4657.2961039642. The cubic root of 21690407 is about 278.8833374438.

The spelling of 21690407 in words is "twenty-one million, six hundred ninety thousand, four hundred seven".