20721900 has 36 divisors (see below), whose sum is σ = 59956232. Its totient is φ = 5525760.

The previous prime is 20721893. The next prime is 20721901. The reversal of 20721900 is 912702.

It is a happy number.

It is a super-2 number, since 2×20721900² = 858794279220000, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (20721901) 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, 34237 + ... + 34836.

Almost surely, 2^20721900 is an apocalyptic number.

20721900 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20721900 is an abundant number, since it is smaller than the sum of its proper divisors (39234332).

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

20721900 is a wasteful number, since it uses less digits than its factorization.

20721900 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69090 (or 69083 counting only the distinct ones).

The product of its (nonzero) digits is 252, while the sum is 21.

The square root of 20721900 is about 4552.1313689304. The cubic root of 20721900 is about 274.6691337584.

The spelling of 20721900 in words is "twenty million, seven hundred twenty-one thousand, nine hundred".