21520213 has 12 divisors (see below), whose sum is σ = 25475884. Its totient is φ = 18057600.

The previous prime is 21520207. The next prime is 21520229. The reversal of 21520213 is 31202512.

It can be written as a sum of positive squares in 2 ways, for example, as 12236004 + 9284209 = 3498^2 + 3047^2 .

It is not a de Polignac number, because 21520213 - 2¹⁷ = 21389141 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520243) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5268 + ... + 8413.

Almost surely, 2^21520213 is an apocalyptic number.

It is an amenable number.

21520213 is a deficient number, since it is larger than the sum of its proper divisors (3955671).

21520213 is a wasteful number, since it uses less digits than its factorization.

21520213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13716 (or 13705 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21520213 is about 4638.9883595456. The cubic root of 21520213 is about 278.1520009640.

Adding to 21520213 its reverse (31202512), we get a palindrome (52722725).

The spelling of 21520213 in words is "twenty-one million, five hundred twenty thousand, two hundred thirteen".