21390831 has 32 divisors (see below), whose sum is σ = 39513600. Its totient is φ = 11111040.

The previous prime is 21390797. The next prime is 21390833. The reversal of 21390831 is 13809312.

It is not a de Polignac number, because 21390831 - 2⁶ = 21390767 is a prime.

It is a super-2 number, since 2×21390831² = 915135301741122, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a junction number, because it is equal to n+sod(n) for n = 21390795 and 21390804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390833) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3066 + ... + 7223.

It is an arithmetic number, because the mean of its divisors is an integer number (1234800).

Almost surely, 2^21390831 is an apocalyptic number.

21390831 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21390831 is a deficient number, since it is larger than the sum of its proper divisors (18122769).

21390831 is a wasteful number, since it uses less digits than its factorization.

21390831 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10316 (or 10310 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21390831 is about 4625.0222702167. The cubic root of 21390831 is about 277.5934528198.

The spelling of 21390831 in words is "twenty-one million, three hundred ninety thousand, eight hundred thirty-one".