21085920 has 120 divisors (see below), whose sum is σ = 74461464. Its totient is φ = 5619456.

The previous prime is 21085919. The next prime is 21085943. The reversal of 21085920 is 2958012.

21085920 = 80² + 81² + ... + 399².

It is a tau number, because it is divible by the number of its divisors (120).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 12147 + ... + 13773.

Almost surely, 2^21085920 is an apocalyptic number.

21085920 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 21085920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37230732).

21085920 is an abundant number, since it is smaller than the sum of its proper divisors (53375544).

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

21085920 is a wasteful number, since it uses less digits than its factorization.

21085920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1654 (or 1637 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 21085920 is about 4591.9407661685. The cubic root of 21085920 is about 276.2681703547.

The spelling of 21085920 in words is "twenty-one million, eighty-five thousand, nine hundred twenty".