21018537 has 6 divisors (see below), whose sum is σ = 30360122. Its totient is φ = 14012352.

The previous prime is 21018523. The next prime is 21018539. The reversal of 21018537 is 73581012.

It can be written as a sum of positive squares in only one way, i.e., 14561856 + 6456681 = 3816^2 + 2541^2 .

It is not a de Polignac number, because 21018537 - 2¹⁶ = 20953001 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21018537.

It is not an unprimeable number, because it can be changed into a prime (21018539) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1167688 + ... + 1167705.

Almost surely, 2^21018537 is an apocalyptic number.

It is an amenable number.

21018537 is a deficient number, since it is larger than the sum of its proper divisors (9341585).

21018537 is a wasteful number, since it uses less digits than its factorization.

21018537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2335399 (or 2335396 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21018537 is about 4584.5978013344. The cubic root of 21018537 is about 275.9735718236.

Adding to 21018537 its reverse (73581012), we get a palindrome (94599549).

The spelling of 21018537 in words is "twenty-one million, eighteen thousand, five hundred thirty-seven".