21243775 has 24 divisors (see below), whose sum is σ = 30292704. Its totient is φ = 14476800.

The previous prime is 21243769. The next prime is 21243779. The reversal of 21243775 is 57734212.

It is not a de Polignac number, because 21243775 - 2⁹ = 21243263 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 (21243779) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 40515 + ... + 41035.

It is an arithmetic number, because the mean of its divisors is an integer number (1262196).

Almost surely, 2^21243775 is an apocalyptic number.

21243775 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21243775 is a deficient number, since it is larger than the sum of its proper divisors (9048929).

21243775 is a wasteful number, since it uses less digits than its factorization.

21243775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 771 (or 766 counting only the distinct ones).

The product of its digits is 11760, while the sum is 31.

The square root of 21243775 is about 4609.0969831411. The cubic root of 21243775 is about 276.9558636295.

Adding to 21243775 its reverse (57734212), we get a palindrome (78977987).

The spelling of 21243775 in words is "twenty-one million, two hundred forty-three thousand, seven hundred seventy-five".