21991684 has 24 divisors (see below), whose sum is σ = 45214848. Its totient is φ = 9227040.

The previous prime is 21991649. The next prime is 21991691. The reversal of 21991684 is 48619912.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18652 + ... + 19795.

It is an arithmetic number, because the mean of its divisors is an integer number (1883952).

Almost surely, 2^21991684 is an apocalyptic number.

It is an amenable number.

21991684 is an abundant number, since it is smaller than the sum of its proper divisors (23223164).

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

21991684 is a wasteful number, since it uses less digits than its factorization.

21991684 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38475 (or 38473 counting only the distinct ones).

The product of its digits is 31104, while the sum is 40.

The square root of 21991684 is about 4689.5291874558. The cubic root of 21991684 is about 280.1686229205.

It can be divided in two parts, 2199 and 1684, that added together give a palindrome (3883).

The spelling of 21991684 in words is "twenty-one million, nine hundred ninety-one thousand, six hundred eighty-four".