21870840 has 128 divisors (see below), whose sum is σ = 70917120. Its totient is φ = 5376000.

The previous prime is 21870829. The next prime is 21870847. The reversal of 21870840 is 4807812.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21870798 and 21870807.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21870847) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 144765 + ... + 144915.

It is an arithmetic number, because the mean of its divisors is an integer number (554040).

Almost surely, 2^21870840 is an apocalyptic number.

21870840 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 21870840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35458560).

21870840 is an abundant number, since it is smaller than the sum of its proper divisors (49046280).

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

21870840 is a wasteful number, since it uses less digits than its factorization.

21870840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 253 (or 249 counting only the distinct ones).

The product of its (nonzero) digits is 3584, while the sum is 30.

The square root of 21870840 is about 4676.6269896155. The cubic root of 21870840 is about 279.6545058402.

21870840 divided by its sum of digits (30) gives a triangular number (729028 = T₁₂₀₇).

The spelling of 21870840 in words is "twenty-one million, eight hundred seventy thousand, eight hundred forty".