21500051 has 4 divisors (see below), whose sum is σ = 21637152. Its totient is φ = 21362952.

The previous prime is 21500029. The next prime is 21500069. The reversal of 21500051 is 15000512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21500051 - 2²² = 17305747 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21499999 and 21500035.

It is not an unprimeable number, because it can be changed into a prime (21500021) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 68315 + ... + 68628.

It is an arithmetic number, because the mean of its divisors is an integer number (5409288).

Almost surely, 2^21500051 is an apocalyptic number.

21500051 is a deficient number, since it is larger than the sum of its proper divisors (137101).

21500051 is a wasteful number, since it uses less digits than its factorization.

21500051 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137100.

The product of its (nonzero) digits is 50, while the sum is 14.

The square root of 21500051 is about 4636.8147472160. The cubic root of 21500051 is about 278.0651081911.

Adding to 21500051 its reverse (15000512), we get a palindrome (36500563).

The spelling of 21500051 in words is "twenty-one million, five hundred thousand, fifty-one".