21813387 has 16 divisors (see below), whose sum is σ = 31445760. Its totient is φ = 13403232.

The previous prime is 21813383. The next prime is 21813403. The reversal of 21813387 is 78331812.

It is not a de Polignac number, because 21813387 - 2² = 21813383 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21813383) 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, 3063 + ... + 7280.

It is an arithmetic number, because the mean of its divisors is an integer number (1965360).

Almost surely, 2^21813387 is an apocalyptic number.

21813387 is a deficient number, since it is larger than the sum of its proper divisors (9632373).

21813387 is a wasteful number, since it uses less digits than its factorization.

21813387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10402.

The product of its digits is 8064, while the sum is 33.

The square root of 21813387 is about 4670.4803821449. The cubic root of 21813387 is about 279.4094142052.

The spelling of 21813387 in words is "twenty-one million, eight hundred thirteen thousand, three hundred eighty-seven".