21387777 has 4 divisors (see below), whose sum is σ = 28517040. Its totient is φ = 14258516.

The previous prime is 21387763. The next prime is 21387803. The reversal of 21387777 is 77778312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21387777 - 2¹⁶ = 21322241 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21387757) 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, 3564627 + ... + 3564632.

It is an arithmetic number, because the mean of its divisors is an integer number (7129260).

Almost surely, 2^21387777 is an apocalyptic number.

It is an amenable number.

21387777 is a deficient number, since it is larger than the sum of its proper divisors (7129263).

21387777 is an equidigital number, since it uses as much as digits as its factorization.

21387777 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7129262.

The product of its digits is 115248, while the sum is 42.

The square root of 21387777 is about 4624.6920978591. The cubic root of 21387777 is about 277.5802413842.

It can be divided in two parts, 213 and 87777, that added together give a triangular number (87990 = T₄₁₉).

The spelling of 21387777 in words is "twenty-one million, three hundred eighty-seven thousand, seven hundred seventy-seven".