20989840 has 40 divisors (see below), whose sum is σ = 49639680. Its totient is φ = 8251776.

The previous prime is 20989807. The next prime is 20989847. The reversal of 20989840 is 4898902.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (40).

It is a hoax number, since the sum of its digits (40) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is a junction number, because it is equal to n+sod(n) for n = 20989793 and 20989802.

It is not an unprimeable number, because it can be changed into a prime (20989847) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2497 + ... + 6943.

It is an arithmetic number, because the mean of its divisors is an integer number (1240992).

Almost surely, 2^20989840 is an apocalyptic number.

20989840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20989840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24819840).

20989840 is an abundant number, since it is smaller than the sum of its proper divisors (28649840).

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

20989840 is a wasteful number, since it uses less digits than its factorization.

20989840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4519 (or 4513 counting only the distinct ones).

The product of its (nonzero) digits is 41472, while the sum is 40.

The square root of 20989840 is about 4581.4670139596. The cubic root of 20989840 is about 275.8479173344.

The spelling of 20989840 in words is "twenty million, nine hundred eighty-nine thousand, eight hundred forty".