21345640 has 16 divisors (see below), whose sum is σ = 48027780. Its totient is φ = 8538240.

The previous prime is 21345637. The next prime is 21345703. The reversal of 21345640 is 4654312.

It can be written as a sum of positive squares in 2 ways, for example, as 21288996 + 56644 = 4614^2 + 238^2 .

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, 266781 + ... + 266860.

Almost surely, 2^21345640 is an apocalyptic number.

21345640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21345640 is an abundant number, since it is smaller than the sum of its proper divisors (26682140).

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

21345640 is a wasteful number, since it uses less digits than its factorization.

21345640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 533652 (or 533648 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 25.

The square root of 21345640 is about 4620.1341971852. The cubic root of 21345640 is about 277.3978305264.

Adding to 21345640 its reverse (4654312), we get a palindrome (25999952).

The spelling of 21345640 in words is "twenty-one million, three hundred forty-five thousand, six hundred forty".