20981664 has 144 divisors (see below), whose sum is σ = 67223520. Its totient is φ = 6151680.

The previous prime is 20981663. The next prime is 20981671. The reversal of 20981664 is 46618902.

It is a tau number, because it is divible by the number of its divisors (144).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (20981663) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 117127 + ... + 117305.

It is an arithmetic number, because the mean of its divisors is an integer number (466830).

Almost surely, 2^20981664 is an apocalyptic number.

20981664 is a gapful number since it is divisible by the number (24) 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 20981664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33611760).

20981664 is an abundant number, since it is smaller than the sum of its proper divisors (46241856).

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

20981664 is a wasteful number, since it uses less digits than its factorization.

20981664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 243 (or 232 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 20981664 is about 4580.5746364403. The cubic root of 20981664 is about 275.8120964250.

The spelling of 20981664 in words is "twenty million, nine hundred eighty-one thousand, six hundred sixty-four".