21220731 has 16 divisors (see below), whose sum is σ = 35929600. Its totient is φ = 12126024.

The previous prime is 21220711. The next prime is 21220733. The reversal of 21220731 is 13702212.

It is not a de Polignac number, because 21220731 - 2⁹ = 21220219 is a prime.

It is a super-2 number, since 2×21220731² = 900638848348722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21220733) 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, 55951 + ... + 56328.

It is an arithmetic number, because the mean of its divisors is an integer number (2245600).

Almost surely, 2^21220731 is an apocalyptic number.

21220731 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21220731 is a deficient number, since it is larger than the sum of its proper divisors (14708869).

21220731 is a wasteful number, since it uses less digits than its factorization.

21220731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 112295 (or 112289 counting only the distinct ones).

The product of its (nonzero) digits is 168, while the sum is 18.

The square root of 21220731 is about 4606.5964659388. The cubic root of 21220731 is about 276.8556855776.

Adding to 21220731 its reverse (13702212), we get a palindrome (34922943).

The spelling of 21220731 in words is "twenty-one million, two hundred twenty thousand, seven hundred thirty-one".