21687318 has 32 divisors (see below), whose sum is σ = 48405600. Its totient is φ = 7197408.

The previous prime is 21687307. The next prime is 21687329. The reversal of 21687318 is 81378612.

It is an interprime number because it is at equal distance from previous prime (21687307) and next prime (21687329).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13780 + ... + 15272.

It is an arithmetic number, because the mean of its divisors is an integer number (1512675).

Almost surely, 2^21687318 is an apocalyptic number.

21687318 is an abundant number, since it is smaller than the sum of its proper divisors (26718282).

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

21687318 is a wasteful number, since it uses less digits than its factorization.

21687318 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1773 (or 1767 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 21687318 is about 4656.9644619645. The cubic root of 21687318 is about 278.8700979269.

The spelling of 21687318 in words is "twenty-one million, six hundred eighty-seven thousand, three hundred eighteen".