21390215 has 24 divisors (see below), whose sum is σ = 32577552. Its totient is φ = 13332480.

The previous prime is 21390163. The next prime is 21390247. The reversal of 21390215 is 51209312.

It is not a de Polignac number, because 21390215 - 2²² = 17195911 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1274 + ... + 6663.

It is an arithmetic number, because the mean of its divisors is an integer number (1357398).

Almost surely, 2^21390215 is an apocalyptic number.

21390215 is a deficient number, since it is larger than the sum of its proper divisors (11187337).

21390215 is a wasteful number, since it uses less digits than its factorization.

21390215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7967 (or 7960 counting only the distinct ones).

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21390215 is about 4624.9556754633. The cubic root of 21390215 is about 277.5907881390.

Adding to 21390215 its reverse (51209312), we get a palindrome (72599527).

The spelling of 21390215 in words is "twenty-one million, three hundred ninety thousand, two hundred fifteen".