21390137 has 4 divisors (see below), whose sum is σ = 21436800. Its totient is φ = 21343476.

The previous prime is 21390133. The next prime is 21390163. The reversal of 21390137 is 73109312.

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 21390137 - 2² = 21390133 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21390133) 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, 22637 + ... + 23562.

It is an arithmetic number, because the mean of its divisors is an integer number (5359200).

Almost surely, 2^21390137 is an apocalyptic number.

It is an amenable number.

21390137 is a deficient number, since it is larger than the sum of its proper divisors (46663).

21390137 is an equidigital number, since it uses as much as digits as its factorization.

21390137 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46662.

The product of its (nonzero) digits is 1134, while the sum is 26.

The square root of 21390137 is about 4624.9472429423. The cubic root of 21390137 is about 277.5904507245.

Adding to 21390137 its reverse (73109312), we get a palindrome (94499449).

The spelling of 21390137 in words is "twenty-one million, three hundred ninety thousand, one hundred thirty-seven".