21228131 has 4 divisors (see below), whose sum is σ = 21246792. Its totient is φ = 21209472.

The previous prime is 21228101. The next prime is 21228133. The reversal of 21228131 is 13182212.

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 21228131 - 2²² = 17033827 is a prime.

It is a super-2 number, since 2×21228131² = 901267091506322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21228133) 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 in 3 ways as a sum of consecutive naturals, for example, 7505 + ... + 9938.

It is an arithmetic number, because the mean of its divisors is an integer number (5311698).

Almost surely, 2^21228131 is an apocalyptic number.

21228131 is a deficient number, since it is larger than the sum of its proper divisors (18661).

21228131 is a wasteful number, since it uses less digits than its factorization.

21228131 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18660.

The product of its digits is 192, while the sum is 20.

The square root of 21228131 is about 4607.3995919607. The cubic root of 21228131 is about 276.8878631367.

The spelling of 21228131 in words is "twenty-one million, two hundred twenty-eight thousand, one hundred thirty-one".