21131811 has 12 divisors (see below), whose sum is σ = 31173792. Its totient is φ = 13787856.

The previous prime is 21131797. The next prime is 21131813. The reversal of 21131811 is 11813112.

It is a happy number.

It is not a de Polignac number, because 21131811 - 2¹⁴ = 21115427 is a prime.

It is a super-2 number, since 2×21131811² = 893106872279442, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21131813) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 24556 + ... + 25401.

It is an arithmetic number, because the mean of its divisors is an integer number (2597816).

Almost surely, 2^21131811 is an apocalyptic number.

21131811 is a deficient number, since it is larger than the sum of its proper divisors (10041981).

21131811 is a wasteful number, since it uses less digits than its factorization.

21131811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50010 (or 50007 counting only the distinct ones).

The product of its digits is 48, while the sum is 18.

The square root of 21131811 is about 4596.9349571209. The cubic root of 21131811 is about 276.4684467502.

Adding to 21131811 its reverse (11813112), we get a palindrome (32944923).

It can be divided in two parts, 2 and 1131811, that multiplied together give a palindrome (2263622).

The spelling of 21131811 in words is "twenty-one million, one hundred thirty-one thousand, eight hundred eleven".