21249987 has 16 divisors (see below), whose sum is σ = 30989952. Its totient is φ = 12845120.

The previous prime is 21249967. The next prime is 21249997. The reversal of 21249987 is 78994212.

It is a cyclic number.

It is not a de Polignac number, because 21249987 - 2⁸ = 21249731 is a prime.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (21249937) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18823 + ... + 19919.

It is an arithmetic number, because the mean of its divisors is an integer number (1936872).

Almost surely, 2^21249987 is an apocalyptic number.

21249987 is a deficient number, since it is larger than the sum of its proper divisors (9739965).

21249987 is a wasteful number, since it uses less digits than its factorization.

21249987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1698.

The product of its digits is 72576, while the sum is 42.

The square root of 21249987 is about 4609.7708185983. The cubic root of 21249987 is about 276.9828563549.

The spelling of 21249987 in words is "twenty-one million, two hundred forty-nine thousand, nine hundred eighty-seven".