20921220 has 192 divisors, whose sum is σ = 71850240. Its totient is φ = 5031936.

The previous prime is 20921161. The next prime is 20921221. The reversal of 20921220 is 2212902.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 20921193 and 20921202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20921221) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 394714 + ... + 394766.

It is an arithmetic number, because the mean of its divisors is an integer number (374220).

Almost surely, 2^20921220 is an apocalyptic number.

20921220 is a gapful number since it is divisible by the number (20) 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 20921220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35925120).

20921220 is an abundant number, since it is smaller than the sum of its proper divisors (50929020).

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

20921220 is a wasteful number, since it uses less digits than its factorization.

20921220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 131 (or 123 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 20921220 is about 4573.9720156555. The cubic root of 20921220 is about 275.5469884269.

The spelling of 20921220 in words is "twenty million, nine hundred twenty-one thousand, two hundred twenty".