21378440 has 32 divisors (see below), whose sum is σ = 48363480. Its totient is φ = 8504832.

The previous prime is 21378421. The next prime is 21378443. The reversal of 21378440 is 4487312.

It can be written as a sum of positive squares in 4 ways, for example, as 20593444 + 784996 = 4538^2 + 886^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21378443) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6524 + ... + 9236.

Almost surely, 2^21378440 is an apocalyptic number.

21378440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21378440 is an abundant number, since it is smaller than the sum of its proper divisors (26985040).

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

21378440 is a wasteful number, since it uses less digits than its factorization.

21378440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2921 (or 2917 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 29.

The square root of 21378440 is about 4623.6825150523. The cubic root of 21378440 is about 277.5398422354.

The spelling of 21378440 in words is "twenty-one million, three hundred seventy-eight thousand, four hundred forty".