21510740 has 12 divisors (see below), whose sum is σ = 45172596. Its totient is φ = 8604288.

The previous prime is 21510733. The next prime is 21510743. The reversal of 21510740 is 4701512.

It can be written as a sum of positive squares in 2 ways, for example, as 11600836 + 9909904 = 3406^2 + 3148^2 .

It is a Harshad number since it is a multiple of its sum of digits (20), and also a Moran number because the ratio is a prime number: 1075537 = 21510740 / (2 + 1 + 5 + 1 + 0 + 7 + 4 + 0).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21510743) 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, 537749 + ... + 537788.

It is an arithmetic number, because the mean of its divisors is an integer number (3764383).

Almost surely, 2^21510740 is an apocalyptic number.

21510740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21510740 is an abundant number, since it is smaller than the sum of its proper divisors (23661856).

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

21510740 is a wasteful number, since it uses less digits than its factorization.

21510740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1075546 (or 1075544 counting only the distinct ones).

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21510740 is about 4637.9672271373. The cubic root of 21510740 is about 278.1111816558. Note that the first 4 decimals are identical.

The spelling of 21510740 in words is "twenty-one million, five hundred ten thousand, seven hundred forty".