20991456 has 72 divisors (see below), whose sum is σ = 62309520. Its totient is φ = 6690816.

The previous prime is 20991437. The next prime is 20991457. The reversal of 20991456 is 65419902.

It is a tau number, because it is divible by the number of its divisors (72).

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

It is a self number, because there is not a number n which added to its sum of digits gives 20991456.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991457) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5040 + ... + 8208.

It is an arithmetic number, because the mean of its divisors is an integer number (865410).

Almost surely, 2^20991456 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20991456, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31154760).

20991456 is an abundant number, since it is smaller than the sum of its proper divisors (41318064).

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

20991456 is a wasteful number, since it uses less digits than its factorization.

20991456 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3208 (or 3197 counting only the distinct ones).

The product of its (nonzero) digits is 19440, while the sum is 36.

The square root of 20991456 is about 4581.6433732887. The cubic root of 20991456 is about 275.8549962957.

The spelling of 20991456 in words is "twenty million, nine hundred ninety-one thousand, four hundred fifty-six".