21172811 has 16 divisors (see below), whose sum is σ = 24572160. Its totient is φ = 18052320.

The previous prime is 21172807. The next prime is 21172819. The reversal of 21172811 is 11827112.

It is not a de Polignac number, because 21172811 - 2² = 21172807 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21172819) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12620 + ... + 14198.

It is an arithmetic number, because the mean of its divisors is an integer number (1535760).

Almost surely, 2^21172811 is an apocalyptic number.

21172811 is a deficient number, since it is larger than the sum of its proper divisors (3399349).

21172811 is a wasteful number, since it uses less digits than its factorization.

21172811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1666.

The product of its digits is 224, while the sum is 23.

The square root of 21172811 is about 4601.3922892968. The cubic root of 21172811 is about 276.6471328606.

Adding to 21172811 its reverse (11827112), we get a palindrome (32999923).

The spelling of 21172811 in words is "twenty-one million, one hundred seventy-two thousand, eight hundred eleven".