21247540 has 24 divisors (see below), whose sum is σ = 44946720. Its totient is φ = 8436768.

The previous prime is 21247537. The next prime is 21247543. The reversal of 21247540 is 4574212.

It is an interprime number because it is at equal distance from previous prime (21247537) and next prime (21247543).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21247543) 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, 1042 + ... + 6601.

It is an arithmetic number, because the mean of its divisors is an integer number (1872780).

Almost surely, 2^21247540 is an apocalyptic number.

21247540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21247540 is an abundant number, since it is smaller than the sum of its proper divisors (23699180).

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

21247540 is a wasteful number, since it uses less digits than its factorization.

21247540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7791 (or 7789 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 25.

The square root of 21247540 is about 4609.5053964607. The cubic root of 21247540 is about 276.9722241434.

The spelling of 21247540 in words is "twenty-one million, two hundred forty-seven thousand, five hundred forty".