21399440 has 20 divisors (see below), whose sum is σ = 49753884. Its totient is φ = 8559744.

The previous prime is 21399437. The next prime is 21399457. The reversal of 21399440 is 4499312.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 2598544 + 18800896 = 1612^2 + 4336^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 21399397 and 21399406.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 133667 + ... + 133826.

Almost surely, 2^21399440 is an apocalyptic number.

21399440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21399440 is an abundant number, since it is smaller than the sum of its proper divisors (28354444).

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

21399440 is a wasteful number, since it uses less digits than its factorization.

21399440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 267506 (or 267500 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 32.

The square root of 21399440 is about 4625.9528748140. The cubic root of 21399440 is about 277.6306881116.

The spelling of 21399440 in words is "twenty-one million, three hundred ninety-nine thousand, four hundred forty".