21087877 has 4 divisors (see below), whose sum is σ = 21098700. Its totient is φ = 21077056.

The previous prime is 21087863. The next prime is 21087889. The reversal of 21087877 is 77878012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 17969121 + 3118756 = 4239^2 + 1766^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21087877 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21087827) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1588 + ... + 6685.

It is an arithmetic number, because the mean of its divisors is an integer number (5274675).

Almost surely, 2^21087877 is an apocalyptic number.

It is an amenable number.

21087877 is a deficient number, since it is larger than the sum of its proper divisors (10823).

21087877 is an equidigital number, since it uses as much as digits as its factorization.

21087877 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10822.

The product of its (nonzero) digits is 43904, while the sum is 40.

The square root of 21087877 is about 4592.1538519523. The cubic root of 21087877 is about 276.2767169754.

The spelling of 21087877 in words is "twenty-one million, eighty-seven thousand, eight hundred seventy-seven".