21959819 has 4 divisors (see below), whose sum is σ = 25096944. Its totient is φ = 18822696.

The previous prime is 21959797. The next prime is 21959837. The reversal of 21959819 is 91895912.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21959819 - 2²⁰ = 20911243 is a prime.

It is a super-2 number, since 2×21959819² = 964467301025522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21959819.

It is not an unprimeable number, because it can be changed into a prime (21959419) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1568552 + ... + 1568565.

It is an arithmetic number, because the mean of its divisors is an integer number (6274236).

Almost surely, 2^21959819 is an apocalyptic number.

21959819 is a deficient number, since it is larger than the sum of its proper divisors (3137125).

21959819 is an equidigital number, since it uses as much as digits as its factorization.

21959819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3137124.

The product of its digits is 58320, while the sum is 44.

The square root of 21959819 is about 4686.1304932748. The cubic root of 21959819 is about 280.0332401014.

The spelling of 21959819 in words is "twenty-one million, nine hundred fifty-nine thousand, eight hundred nineteen".