21821031 has 6 divisors (see below), whose sum is σ = 31519280. Its totient is φ = 14547348.

The previous prime is 21821027. The next prime is 21821039. The reversal of 21821031 is 13012812.

It is not a de Polignac number, because 21821031 - 2² = 21821027 is a prime.

It is a super-2 number, since 2×21821031² = 952314787805922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21820995 and 21821013.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21821039) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1212271 + ... + 1212288.

Almost surely, 2^21821031 is an apocalyptic number.

21821031 is a deficient number, since it is larger than the sum of its proper divisors (9698249).

21821031 is a wasteful number, since it uses less digits than its factorization.

21821031 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2424565 (or 2424562 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21821031 is about 4671.2986417055. The cubic root of 21821031 is about 279.4420479288.

Adding to 21821031 its reverse (13012812), we get a palindrome (34833843).

The spelling of 21821031 in words is "twenty-one million, eight hundred twenty-one thousand, thirty-one".