21555420 has 48 divisors (see below), whose sum is σ = 60969888. Its totient is φ = 5689600.

The previous prime is 21555407. The next prime is 21555433. The reversal of 21555420 is 2455512.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21555407) and next prime (21555433).

It is a super-2 number, since 2×21555420² = 929272262752800, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4282 + ... + 7838.

It is an arithmetic number, because the mean of its divisors is an integer number (1270206).

Almost surely, 2^21555420 is an apocalyptic number.

21555420 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 21555420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30484944).

21555420 is an abundant number, since it is smaller than the sum of its proper divisors (39414468).

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

21555420 is a wasteful number, since it uses less digits than its factorization.

21555420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3670 (or 3668 counting only the distinct ones).

The product of its (nonzero) digits is 2000, while the sum is 24.

The square root of 21555420 is about 4642.7814938892. The cubic root of 21555420 is about 278.3036035831.

The spelling of 21555420 in words is "twenty-one million, five hundred fifty-five thousand, four hundred twenty".