21540051 has 24 divisors (see below), whose sum is σ = 33991776. Its totient is φ = 13063680.

The previous prime is 21540049. The next prime is 21540059. The reversal of 21540051 is 15004512.

21540051 is a `hidden beast` number, since 215 + 400 + 51 = 666.

It is not a de Polignac number, because 21540051 - 2¹ = 21540049 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21540059) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7011 + ... + 9603.

It is an arithmetic number, because the mean of its divisors is an integer number (1416324).

Almost surely, 2^21540051 is an apocalyptic number.

21540051 is a deficient number, since it is larger than the sum of its proper divisors (12451725).

21540051 is a wasteful number, since it uses less digits than its factorization.

21540051 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2683 (or 2680 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21540051 is about 4641.1260487084. The cubic root of 21540051 is about 278.2374444293.

Adding to 21540051 its reverse (15004512), we get a palindrome (36544563).

The spelling of 21540051 in words is "twenty-one million, five hundred forty thousand, fifty-one".