21987511 has 32 divisors (see below), whose sum is σ = 29248128. Its totient is φ = 16035840.

The previous prime is 21987487. The next prime is 21987523. The reversal of 21987511 is 11578912.

It is a happy number.

It is a 12-Lehmer number, since φ(21987511) divides (21987511-1)¹².

It is a cyclic number.

It is not a de Polignac number, because 21987511 - 2⁵ = 21987479 is a prime.

It is a Smith number, since the sum of its digits (34) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987571) 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 31 ways as a sum of consecutive naturals, for example, 94251 + ... + 94483.

It is an arithmetic number, because the mean of its divisors is an integer number (914004).

Almost surely, 2^21987511 is an apocalyptic number.

21987511 is a deficient number, since it is larger than the sum of its proper divisors (7260617).

21987511 is a wasteful number, since it uses less digits than its factorization.

21987511 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 331.

The product of its digits is 5040, while the sum is 34.

The square root of 21987511 is about 4689.0842389533. The cubic root of 21987511 is about 280.1509008031.

The spelling of 21987511 in words is "twenty-one million, nine hundred eighty-seven thousand, five hundred eleven".