21658420 has 48 divisors (see below), whose sum is σ = 52778880. Its totient is φ = 7311744.

The previous prime is 21658393. The next prime is 21658421. The reversal of 21658420 is 2485612.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21658421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8226 + ... + 10534.

It is an arithmetic number, because the mean of its divisors is an integer number (1099560).

Almost surely, 2^21658420 is an apocalyptic number.

21658420 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 21658420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26389440).

21658420 is an abundant number, since it is smaller than the sum of its proper divisors (31120460).

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

21658420 is a wasteful number, since it uses less digits than its factorization.

21658420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2392 (or 2390 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 28.

The square root of 21658420 is about 4653.8607628506. The cubic root of 21658420 is about 278.7461795746.

It can be divided in two parts, 2165 and 8420, that added together give a triangular number (10585 = T₁₄₅).

The spelling of 21658420 in words is "twenty-one million, six hundred fifty-eight thousand, four hundred twenty".