21780775 has 6 divisors (see below), whose sum is σ = 27008192. Its totient is φ = 17424600.

The previous prime is 21780763. The next prime is 21780779. The reversal of 21780775 is 57708712.

It is not a de Polignac number, because 21780775 - 2⁵ = 21780743 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21780779) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 435591 + ... + 435640.

Almost surely, 2^21780775 is an apocalyptic number.

21780775 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21780775 is a deficient number, since it is larger than the sum of its proper divisors (5227417).

21780775 is an equidigital number, since it uses as much as digits as its factorization.

21780775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 871241 (or 871236 counting only the distinct ones).

The product of its (nonzero) digits is 27440, while the sum is 37.

The square root of 21780775 is about 4666.9877865707. The cubic root of 21780775 is about 279.2701015193.

The spelling of 21780775 in words is "twenty-one million, seven hundred eighty thousand, seven hundred seventy-five".