21213215 has 16 divisors (see below), whose sum is σ = 27371520. Its totient is φ = 15732000.

The previous prime is 21213193. The next prime is 21213251. The reversal of 21213215 is 51231212.

It is a happy number.

It is not a de Polignac number, because 21213215 - 2¹² = 21209119 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21213193 and 21213202.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2090 + ... + 6840.

It is an arithmetic number, because the mean of its divisors is an integer number (1710720).

Almost surely, 2^21213215 is an apocalyptic number.

21213215 is a deficient number, since it is larger than the sum of its proper divisors (6158305).

21213215 is a wasteful number, since it uses less digits than its factorization.

21213215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4822.

The product of its digits is 120, while the sum is 17.

The square root of 21213215 is about 4605.7806070198. The cubic root of 21213215 is about 276.8229959553.

Adding to 21213215 its reverse (51231212), we get a palindrome (72444427).

The spelling of 21213215 in words is "twenty-one million, two hundred thirteen thousand, two hundred fifteen".