21006740 has 12 divisors (see below), whose sum is σ = 44114196. Its totient is φ = 8402688.

The previous prime is 21006737. The next prime is 21006743. The reversal of 21006740 is 4760012.

It is an interprime number because it is at equal distance from previous prime (21006737) and next prime (21006743).

It can be written as a sum of positive squares in 2 ways, for example, as 8868484 + 12138256 = 2978^2 + 3484^2 .

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: 1050337 = 21006740 / (2 + 1 + 0 + 0 + 6 + 7 + 4 + 0).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006743) 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, 525149 + ... + 525188.

It is an arithmetic number, because the mean of its divisors is an integer number (3676183).

Almost surely, 2^21006740 is an apocalyptic number.

21006740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21006740 is an abundant number, since it is smaller than the sum of its proper divisors (23107456).

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

21006740 is a wasteful number, since it uses less digits than its factorization.

21006740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1050346 (or 1050344 counting only the distinct ones).

The product of its (nonzero) digits is 336, while the sum is 20.

The square root of 21006740 is about 4583.3110302488. The cubic root of 21006740 is about 275.9219305904.

Adding to 21006740 its reverse (4760012), we get a palindrome (25766752).

The spelling of 21006740 in words is "twenty-one million, six thousand, seven hundred forty".