21228331 has 2 divisors, whose sum is σ = 21228332. Its totient is φ = 21228330.

The previous prime is 21228307. The next prime is 21228341. The reversal of 21228331 is 13382212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21228331 - 2⁹ = 21227819 is a prime.

It is a super-2 number, since 2×21228331² = 901284074091122, which contains 22 as substring.

It is equal to p_1343443 and since 21228331 and 1343443 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21228341) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10614165 + 10614166.

It is an arithmetic number, because the mean of its divisors is an integer number (10614166).

Almost surely, 2^21228331 is an apocalyptic number.

21228331 is a deficient number, since it is larger than the sum of its proper divisors (1).

21228331 is an equidigital number, since it uses as much as digits as its factorization.

21228331 is an evil number, because the sum of its binary digits is even.

The product of its digits is 576, while the sum is 22.

The square root of 21228331 is about 4607.4212961265. The cubic root of 21228331 is about 276.8887326967. Note that the first 3 decimals are identical.

The spelling of 21228331 in words is "twenty-one million, two hundred twenty-eight thousand, three hundred thirty-one".