21637920 has 96 divisors (see below), whose sum is σ = 69370560. Its totient is φ = 5667840.

The previous prime is 21637919. The next prime is 21637921. The reversal of 21637920 is 2973612.

It is an interprime number because it is at equal distance from previous prime (21637919) and next prime (21637921).

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21637921) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28911 + ... + 29649.

It is an arithmetic number, because the mean of its divisors is an integer number (722610).

Almost surely, 2^21637920 is an apocalyptic number.

21637920 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 21637920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34685280).

21637920 is an abundant number, since it is smaller than the sum of its proper divisors (47732640).

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

21637920 is a wasteful number, since it uses less digits than its factorization.

21637920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 818 (or 810 counting only the distinct ones).

The product of its (nonzero) digits is 4536, while the sum is 30.

The square root of 21637920 is about 4651.6577690110. The cubic root of 21637920 is about 278.6582060825.

The spelling of 21637920 in words is "twenty-one million, six hundred thirty-seven thousand, nine hundred twenty".