21331506 has 32 divisors (see below), whose sum is σ = 49241088. Its totient is φ = 6034320.

The previous prime is 21331487. The next prime is 21331523. The reversal of 21331506 is 60513312.

It is a Harshad number since it is a multiple of its sum of digits (21).

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 in 15 ways as a sum of consecutive naturals, for example, 1861 + ... + 6791.

It is an arithmetic number, because the mean of its divisors is an integer number (1538784).

Almost surely, 2^21331506 is an apocalyptic number.

21331506 is an abundant number, since it is smaller than the sum of its proper divisors (27909582).

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

21331506 is a wasteful number, since it uses less digits than its factorization.

21331506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5046.

The product of its (nonzero) digits is 540, while the sum is 21.

The square root of 21331506 is about 4618.6043346448. The cubic root of 21331506 is about 277.3365907506.

Adding to 21331506 its reverse (60513312), we get a palindrome (81844818).

The spelling of 21331506 in words is "twenty-one million, three hundred thirty-one thousand, five hundred six".