21154765 has 4 divisors (see below), whose sum is σ = 25385724. Its totient is φ = 16923808.

The previous prime is 21154759. The next prime is 21154789. The reversal of 21154765 is 56745112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 5560164 + 15594601 = 2358^2 + 3949^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21154765 is a prime.

It is a Smith number, since the sum of its digits (31) 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 an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2115472 + ... + 2115481.

It is an arithmetic number, because the mean of its divisors is an integer number (6346431).

Almost surely, 2^21154765 is an apocalyptic number.

It is an amenable number.

21154765 is a deficient number, since it is larger than the sum of its proper divisors (4230959).

21154765 is an equidigital number, since it uses as much as digits as its factorization.

21154765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4230958.

The product of its digits is 8400, while the sum is 31.

The square root of 21154765 is about 4599.4309430624. The cubic root of 21154765 is about 276.5685132700.

Adding to 21154765 its reverse (56745112), we get a palindrome (77899877).

The spelling of 21154765 in words is "twenty-one million, one hundred fifty-four thousand, seven hundred sixty-five".