21538506 has 32 divisors (see below), whose sum is σ = 47190528. Its totient is φ = 6499440.

The previous prime is 21538499. The next prime is 21538519. The reversal of 21538506 is 60583512.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 19731 + ... + 20793.

It is an arithmetic number, because the mean of its divisors is an integer number (1474704).

Almost surely, 2^21538506 is an apocalyptic number.

21538506 is an abundant number, since it is smaller than the sum of its proper divisors (25652022).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21538506 is a wasteful number, since it uses less digits than its factorization.

21538506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1386.

The product of its (nonzero) digits is 7200, while the sum is 30.

The square root of 21538506 is about 4640.9595990485. The cubic root of 21538506 is about 278.2307919051.

The spelling of 21538506 in words is "twenty-one million, five hundred thirty-eight thousand, five hundred six".