21507213 has 16 divisors (see below), whose sum is σ = 35294336. Its totient is φ = 11344320.

The previous prime is 21507137. The next prime is 21507217. The reversal of 21507213 is 31270512.

It is not a de Polignac number, because 21507213 - 2¹³ = 21499021 is a prime.

It is a super-2 number, since 2×21507213² = 925120422054738, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a self number, because there is not a number n which added to its sum of digits gives 21507213.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21507217) 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, 39118 + ... + 39663.

It is an arithmetic number, because the mean of its divisors is an integer number (2205896).

Almost surely, 2^21507213 is an apocalyptic number.

It is an amenable number.

21507213 is a deficient number, since it is larger than the sum of its proper divisors (13787123).

21507213 is a wasteful number, since it uses less digits than its factorization.

21507213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78804.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21507213 is about 4637.5869803164. The cubic root of 21507213 is about 278.0959806949.

Adding to 21507213 its reverse (31270512), we get a palindrome (52777725).

The spelling of 21507213 in words is "twenty-one million, five hundred seven thousand, two hundred thirteen".