21138775 has 24 divisors (see below), whose sum is σ = 30156800. Its totient is φ = 14398560.

The previous prime is 21138751. The next prime is 21138781. The reversal of 21138775 is 57783112.

21138775 = T₁₀₆ + T₁₀₇ + ... + T₅₀₃.

It is not a de Polignac number, because 21138775 - 2²¹ = 19041623 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21138775.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 34522 + ... + 35128.

Almost surely, 2^21138775 is an apocalyptic number.

21138775 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21138775 is a deficient number, since it is larger than the sum of its proper divisors (9018025).

21138775 is a wasteful number, since it uses less digits than its factorization.

21138775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 823 (or 818 counting only the distinct ones).

The product of its digits is 11760, while the sum is 34.

The square root of 21138775 is about 4597.6923559542. The cubic root of 21138775 is about 276.4988135245.

The spelling of 21138775 in words is "twenty-one million, one hundred thirty-eight thousand, seven hundred seventy-five".