21006775 has 12 divisors (see below), whose sum is σ = 26295192. Its totient is φ = 16646240.

The previous prime is 21006743. The next prime is 21006779. The reversal of 21006775 is 57760012.

It is not a de Polignac number, because 21006775 - 2⁵ = 21006743 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 (21006779) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1252 + ... + 6601.

It is an arithmetic number, because the mean of its divisors is an integer number (2191266).

Almost surely, 2^21006775 is an apocalyptic number.

21006775 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21006775 is a deficient number, since it is larger than the sum of its proper divisors (5288417).

21006775 is a wasteful number, since it uses less digits than its factorization.

21006775 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7970 (or 7965 counting only the distinct ones).

The product of its (nonzero) digits is 2940, while the sum is 28.

The square root of 21006775 is about 4583.3148484476. The cubic root of 21006775 is about 275.9220838311.

Adding to 21006775 its reverse (57760012), we get a palindrome (78766787).

The spelling of 21006775 in words is "twenty-one million, six thousand, seven hundred seventy-five".