21213137 has 4 divisors (see below), whose sum is σ = 23141616. Its totient is φ = 19284660.

The previous prime is 21213119. The next prime is 21213149. The reversal of 21213137 is 73131212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21213137 - 2¹⁶ = 21147601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21213187) 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, 964223 + ... + 964244.

It is an arithmetic number, because the mean of its divisors is an integer number (5785404).

Almost surely, 2^21213137 is an apocalyptic number.

It is an amenable number.

21213137 is a deficient number, since it is larger than the sum of its proper divisors (1928479).

21213137 is a wasteful number, since it uses less digits than its factorization.

21213137 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1928478.

The product of its digits is 252, while the sum is 20.

The square root of 21213137 is about 4605.7721393920. The cubic root of 21213137 is about 276.8226566665.

Adding to 21213137 its reverse (73131212), we get a palindrome (94344349).

The spelling of 21213137 in words is "twenty-one million, two hundred thirteen thousand, one hundred thirty-seven".