21007720 has 16 divisors (see below), whose sum is σ = 47267460. Its totient is φ = 8403072.

The previous prime is 21007709. The next prime is 21007741. The reversal of 21007720 is 2770012.

It can be written as a sum of positive squares in 2 ways, for example, as 20994724 + 12996 = 4582^2 + 114^2 .

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, 262557 + ... + 262636.

Almost surely, 2^21007720 is an apocalyptic number.

21007720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21007720 is an abundant number, since it is smaller than the sum of its proper divisors (26259740).

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

21007720 is a wasteful number, since it uses less digits than its factorization.

21007720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 525204 (or 525200 counting only the distinct ones).

The product of its (nonzero) digits is 196, while the sum is 19.

The square root of 21007720 is about 4583.4179386131. The cubic root of 21007720 is about 275.9262212654.

Adding to 21007720 its reverse (2770012), we get a palindrome (23777732).

The spelling of 21007720 in words is "twenty-one million, seven thousand, seven hundred twenty".