21399538 has 4 divisors (see below), whose sum is σ = 32099310. Its totient is φ = 10699768.

The previous prime is 21399527. The next prime is 21399541. The reversal of 21399538 is 83599312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 13373649 + 8025889 = 3657^2 + 2833^2 .

It is a super-2 number, since 2×21399538² = 915880453226888, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21399538.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5349883 + ... + 5349886.

Almost surely, 2^21399538 is an apocalyptic number.

21399538 is a deficient number, since it is larger than the sum of its proper divisors (10699772).

21399538 is a wasteful number, since it uses less digits than its factorization.

21399538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10699771.

The product of its digits is 58320, while the sum is 40.

The square root of 21399538 is about 4625.9634672142. The cubic root of 21399538 is about 277.6311119197.

The spelling of 21399538 in words is "twenty-one million, three hundred ninety-nine thousand, five hundred thirty-eight".