21778840 has 16 divisors (see below), whose sum is σ = 49002480. Its totient is φ = 8711520.

The previous prime is 21778837. The next prime is 21778843. The reversal of 21778840 is 4887712.

It is an interprime number because it is at equal distance from previous prime (21778837) and next prime (21778843).

It is a self number, because there is not a number n which added to its sum of digits gives 21778840.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21778843) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 272196 + ... + 272275.

It is an arithmetic number, because the mean of its divisors is an integer number (3062655).

Almost surely, 2^21778840 is an apocalyptic number.

21778840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21778840 is an abundant number, since it is smaller than the sum of its proper divisors (27223640).

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

21778840 is a wasteful number, since it uses less digits than its factorization.

21778840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 544482 (or 544478 counting only the distinct ones).

The product of its (nonzero) digits is 25088, while the sum is 37.

The square root of 21778840 is about 4666.7804748027. The cubic root of 21778840 is about 279.2618311731.

The spelling of 21778840 in words is "twenty-one million, seven hundred seventy-eight thousand, eight hundred forty".