21155420 has 72 divisors (see below), whose sum is σ = 52572240. Its totient is φ = 7088640.

The previous prime is 21155419. The next prime is 21155437. The reversal of 21155420 is 2455112.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 21155392 and 21155401.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 36896 + ... + 37464.

It is an arithmetic number, because the mean of its divisors is an integer number (730170).

Almost surely, 2^21155420 is an apocalyptic number.

21155420 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 21155420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26286120).

21155420 is an abundant number, since it is smaller than the sum of its proper divisors (31416820).

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

21155420 is a wasteful number, since it uses less digits than its factorization.

21155420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 615 (or 600 counting only the distinct ones).

The product of its (nonzero) digits is 400, while the sum is 20.

The square root of 21155420 is about 4599.5021469720. The cubic root of 21155420 is about 276.5713676389.

The spelling of 21155420 in words is "twenty-one million, one hundred fifty-five thousand, four hundred twenty".