21681318 has 32 divisors (see below), whose sum is σ = 47635200. Its totient is φ = 6548256.

The previous prime is 21681311. The next prime is 21681347. The reversal of 21681318 is 81318612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681311) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1513 + ... + 6756.

It is an arithmetic number, because the mean of its divisors is an integer number (1488600).

Almost surely, 2^21681318 is an apocalyptic number.

21681318 is an abundant number, since it is smaller than the sum of its proper divisors (25953882).

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

21681318 is a wasteful number, since it uses less digits than its factorization.

21681318 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8316.

The product of its digits is 2304, while the sum is 30.

The square root of 21681318 is about 4656.3202209470. The cubic root of 21681318 is about 278.8443782119.

It can be divided in two parts, 2168 and 1318, that added together give a triangular number (3486 = T₈₃).

The spelling of 21681318 in words is "twenty-one million, six hundred eighty-one thousand, three hundred eighteen".