20721744 has 100 divisors (see below), whose sum is σ = 61216320. Its totient is φ = 6765120.

The previous prime is 20721737. The next prime is 20721749. The reversal of 20721744 is 44712702.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721749) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 76329 + ... + 76599.

Almost surely, 2^20721744 is an apocalyptic number.

20721744 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 20721744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30608160).

20721744 is an abundant number, since it is smaller than the sum of its proper divisors (40494576).

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

20721744 is a wasteful number, since it uses less digits than its factorization.

20721744 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 350 (or 335 counting only the distinct ones).

The product of its (nonzero) digits is 3136, while the sum is 27.

The square root of 20721744 is about 4552.1142340675. The cubic root of 20721744 is about 274.6684444958.

The spelling of 20721744 in words is "twenty million, seven hundred twenty-one thousand, seven hundred forty-four".