21355840 has 56 divisors (see below), whose sum is σ = 55485792. Its totient is φ = 7764480.

The previous prime is 21355837. The next prime is 21355843. The reversal of 21355840 is 4855312.

21355840 = T₁₉₆₅ + T₁₉₆₆ + ... + T₁₉₇₅.

It is an interprime number because it is at equal distance from previous prime (21355837) and next prime (21355843).

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 21355799 and 21355808.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21355843) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 487 + ... + 6553.

Almost surely, 2^21355840 is an apocalyptic number.

21355840 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 21355840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27742896).

21355840 is an abundant number, since it is smaller than the sum of its proper divisors (34129952).

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

21355840 is a wasteful number, since it uses less digits than its factorization.

21355840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6095 (or 6085 counting only the distinct ones).

The product of its (nonzero) digits is 4800, while the sum is 28.

The square root of 21355840 is about 4621.2379293865. The cubic root of 21355840 is about 277.4420082806.

The spelling of 21355840 in words is "twenty-one million, three hundred fifty-five thousand, eight hundred forty".