21005777 has 8 divisors (see below), whose sum is σ = 22993320. Its totient is φ = 19071360.

The previous prime is 21005767. The next prime is 21005779. The reversal of 21005777 is 77750012.

It can be written as a sum of positive squares in 4 ways, for example, as 1256641 + 19749136 = 1121^2 + 4444^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21005777 - 2⁶ = 21005713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21005779) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12452 + ... + 14037.

It is an arithmetic number, because the mean of its divisors is an integer number (2874165).

Almost surely, 2^21005777 is an apocalyptic number.

It is an amenable number.

21005777 is a deficient number, since it is larger than the sum of its proper divisors (1987543).

21005777 is a wasteful number, since it uses less digits than its factorization.

21005777 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26563.

The product of its (nonzero) digits is 3430, while the sum is 29.

The square root of 21005777 is about 4583.2059739881. The cubic root of 21005777 is about 275.9177142154.

Adding to 21005777 its reverse (77750012), we get a palindrome (98755789).

The spelling of 21005777 in words is "twenty-one million, five thousand, seven hundred seventy-seven".