21003812 has 6 divisors (see below), whose sum is σ = 36756678. Its totient is φ = 10501904.

The previous prime is 21003811. The next prime is 21003821. The reversal of 21003812 is 21830012.

It can be written as a sum of positive squares in only one way, i.e., 17255716 + 3748096 = 4154^2 + 1936^2 .

It is not an unprimeable number, because it can be changed into a prime (21003811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2625473 + ... + 2625480.

It is an arithmetic number, because the mean of its divisors is an integer number (6126113).

Almost surely, 2^21003812 is an apocalyptic number.

It is an amenable number.

21003812 is a deficient number, since it is larger than the sum of its proper divisors (15752866).

21003812 is a wasteful number, since it uses less digits than its factorization.

21003812 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5250957 (or 5250955 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 21003812 is about 4582.9915993813. The cubic root of 21003812 is about 275.9091103090.

Adding to 21003812 its reverse (21830012), we get a palindrome (42833824).

The spelling of 21003812 in words is "twenty-one million, three thousand, eight hundred twelve".