21806988 has 48 divisors (see below), whose sum is σ = 61576704. Its totient is φ = 5863680.

The previous prime is 21806987. The next prime is 21806989. The reversal of 21806988 is 88960812.

It is an interprime number because it is at equal distance from previous prime (21806987) and next prime (21806989).

It is a Harshad number since it is a multiple of its sum of digits (42).

It is not an unprimeable number, because it can be changed into a prime (21806987) 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, 6208 + ... + 9063.

It is an arithmetic number, because the mean of its divisors is an integer number (1282848).

Almost surely, 2^21806988 is an apocalyptic number.

21806988 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21806988 is an abundant number, since it is smaller than the sum of its proper divisors (39769716).

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

21806988 is a wasteful number, since it uses less digits than its factorization.

21806988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15302 (or 15300 counting only the distinct ones).

The product of its (nonzero) digits is 55296, while the sum is 42.

The square root of 21806988 is about 4669.7952845922. The cubic root of 21806988 is about 279.3820897660.

The spelling of 21806988 in words is "twenty-one million, eight hundred six thousand, nine hundred eighty-eight".