20721820 has 24 divisors (see below), whose sum is σ = 49732704. Its totient is φ = 7104576.

The previous prime is 20721817. The next prime is 20721871. The reversal of 20721820 is 2812702.

It is a super-2 number, since 2×20721820² = 858787648224800, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 20721791 and 20721800.

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 7 ways as a sum of consecutive naturals, for example, 73867 + ... + 74146.

It is an arithmetic number, because the mean of its divisors is an integer number (2072196).

Almost surely, 2^20721820 is an apocalyptic number.

20721820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20721820 is an abundant number, since it is smaller than the sum of its proper divisors (29010884).

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

20721820 is a wasteful number, since it uses less digits than its factorization.

20721820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 148029 (or 148027 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 22.

The square root of 20721820 is about 4552.1225818293. The cubic root of 20721820 is about 274.6687802908.

The spelling of 20721820 in words is "twenty million, seven hundred twenty-one thousand, eight hundred twenty".