21687320 has 16 divisors (see below), whose sum is σ = 48796560. Its totient is φ = 8674912.

The previous prime is 21687307. The next prime is 21687329. The reversal of 21687320 is 2378612.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21687329) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 271052 + ... + 271131.

It is an arithmetic number, because the mean of its divisors is an integer number (3049785).

Almost surely, 2^21687320 is an apocalyptic number.

21687320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21687320 is an abundant number, since it is smaller than the sum of its proper divisors (27109240).

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

21687320 is a wasteful number, since it uses less digits than its factorization.

21687320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 542194 (or 542190 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 29.

The square root of 21687320 is about 4656.9646766966. The cubic root of 21687320 is about 278.8701064994.

The spelling of 21687320 in words is "twenty-one million, six hundred eighty-seven thousand, three hundred twenty".