21990811 has 4 divisors (see below), whose sum is σ = 22700224. Its totient is φ = 21281400.

The previous prime is 21990799. The next prime is 21990821. The reversal of 21990811 is 11809912.

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 21990811 - 2¹¹ = 21988763 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 709381 = 21990811 / (2 + 1 + 9 + 9 + 0 + 8 + 1 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21990821) 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, 354660 + ... + 354721.

It is an arithmetic number, because the mean of its divisors is an integer number (5675056).

Almost surely, 2^21990811 is an apocalyptic number.

21990811 is a deficient number, since it is larger than the sum of its proper divisors (709413).

21990811 is an equidigital number, since it uses as much as digits as its factorization.

21990811 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 709412.

The product of its (nonzero) digits is 1296, while the sum is 31.

The square root of 21990811 is about 4689.4361068256. The cubic root of 21990811 is about 280.1649156033.

It can be divided in two parts, 21990 and 811, that added together give a square (22801 = 151²).

The spelling of 21990811 in words is "twenty-one million, nine hundred ninety thousand, eight hundred eleven".