21388775 has 24 divisors (see below), whose sum is σ = 28696080. Its totient is φ = 15759360.

The previous prime is 21388769. The next prime is 21388777. The reversal of 21388775 is 57788312.

It is not a de Polignac number, because 21388775 - 2¹² = 21384679 is a prime.

It is a Smith number, since the sum of its digits (41) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21388777) 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, 16967 + ... + 18183.

It is an arithmetic number, because the mean of its divisors is an integer number (1195670).

Almost surely, 2^21388775 is an apocalyptic number.

21388775 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21388775 is a deficient number, since it is larger than the sum of its proper divisors (7307305).

21388775 is a wasteful number, since it uses less digits than its factorization.

21388775 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1283 (or 1278 counting only the distinct ones).

The product of its digits is 94080, while the sum is 41.

The square root of 21388775 is about 4624.7999956755. The cubic root of 21388775 is about 277.5845588155.

It can be divided in two parts, 213 and 88775, that added together give a palindrome (88988).

The spelling of 21388775 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred seventy-five".