21768261 has 4 divisors (see below), whose sum is σ = 29024352. Its totient is φ = 14512172.

The previous prime is 21768251. The next prime is 21768269. The reversal of 21768261 is 16286712.

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 21768261 - 2⁷ = 21768133 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21768269) 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, 3628041 + ... + 3628046.

It is an arithmetic number, because the mean of its divisors is an integer number (7256088).

Almost surely, 2^21768261 is an apocalyptic number.

It is an amenable number.

21768261 is a deficient number, since it is larger than the sum of its proper divisors (7256091).

21768261 is an equidigital number, since it uses as much as digits as its factorization.

21768261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7256090.

The product of its digits is 8064, while the sum is 33.

The square root of 21768261 is about 4665.6469004844. The cubic root of 21768261 is about 279.2166070107.

The spelling of 21768261 in words is "twenty-one million, seven hundred sixty-eight thousand, two hundred sixty-one".