21237813 has 12 divisors (see below), whose sum is σ = 30850560. Its totient is φ = 14078376.

The previous prime is 21237793. The next prime is 21237841. The reversal of 21237813 is 31873212.

It is not a de Polignac number, because 21237813 - 2⁵ = 21237781 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21237113) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4981 + ... + 8202.

It is an arithmetic number, because the mean of its divisors is an integer number (2570880).

Almost surely, 2^21237813 is an apocalyptic number.

It is an amenable number.

21237813 is a deficient number, since it is larger than the sum of its proper divisors (9612747).

21237813 is a wasteful number, since it uses less digits than its factorization.

21237813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13368 (or 13365 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21237813 is about 4608.4501733229. The cubic root of 21237813 is about 276.9299522688.

It can be divided in two parts, 212 and 37813, that added together give a square (38025 = 195²).

The spelling of 21237813 in words is "twenty-one million, two hundred thirty-seven thousand, eight hundred thirteen".