21556538 has 4 divisors (see below), whose sum is σ = 32334810. Its totient is φ = 10778268.

The previous prime is 21556519. The next prime is 21556547. The reversal of 21556538 is 83565512.

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., 16834609 + 4721929 = 4103^2 + 2173^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21556498 and 21556507.

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, 5389133 + ... + 5389136.

Almost surely, 2^21556538 is an apocalyptic number.

21556538 is a deficient number, since it is larger than the sum of its proper divisors (10778272).

21556538 is a wasteful number, since it uses less digits than its factorization.

21556538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10778271.

The product of its digits is 36000, while the sum is 35.

The square root of 21556538 is about 4642.9018942898. The cubic root of 21556538 is about 278.3084150265.

The spelling of 21556538 in words is "twenty-one million, five hundred fifty-six thousand, five hundred thirty-eight".