21506213 has 16 divisors (see below), whose sum is σ = 22982400. Its totient is φ = 20097216.

The previous prime is 21506209. The next prime is 21506257. The reversal of 21506213 is 31260512.

It is not a de Polignac number, because 21506213 - 2² = 21506209 is a prime.

It is a super-3 number, since 3×21506213³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21502213) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 144263 + ... + 144411.

It is an arithmetic number, because the mean of its divisors is an integer number (1436400).

Almost surely, 2^21506213 is an apocalyptic number.

It is an amenable number.

21506213 is a deficient number, since it is larger than the sum of its proper divisors (1476187).

21506213 is a wasteful number, since it uses less digits than its factorization.

21506213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 316.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21506213 is about 4637.4791643737. The cubic root of 21506213 is about 278.0916705085.

Adding to 21506213 its reverse (31260512), we get a palindrome (52766725).

The spelling of 21506213 in words is "twenty-one million, five hundred six thousand, two hundred thirteen".