20721834 has 96 divisors (see below), whose sum is σ = 54587520. Its totient is φ = 5556096.

The previous prime is 20721817. The next prime is 20721871. The reversal of 20721834 is 43812702.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 20721798 and 20721807.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 193609 + ... + 193715.

It is an arithmetic number, because the mean of its divisors is an integer number (568620).

Almost surely, 2^20721834 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20721834, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27293760).

20721834 is an abundant number, since it is smaller than the sum of its proper divisors (33865686).

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

20721834 is a wasteful number, since it uses less digits than its factorization.

20721834 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 204 (or 201 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 20721834 is about 4552.1241195732. The cubic root of 20721834 is about 274.6688421477.

The spelling of 20721834 in words is "twenty million, seven hundred twenty-one thousand, eight hundred thirty-four".