21511051 has 4 divisors (see below), whose sum is σ = 22011352. Its totient is φ = 21010752.

The previous prime is 21511031. The next prime is 21511079. The reversal of 21511051 is 15011512.

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 21511051 - 2⁹ = 21510539 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21511031) 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, 250086 + ... + 250171.

It is an arithmetic number, because the mean of its divisors is an integer number (5502838).

Almost surely, 2^21511051 is an apocalyptic number.

21511051 is a deficient number, since it is larger than the sum of its proper divisors (500301).

21511051 is an equidigital number, since it uses as much as digits as its factorization.

21511051 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 500300.

The product of its (nonzero) digits is 50, while the sum is 16.

The square root of 21511051 is about 4638.0007546356. Note that the first 3 decimals coincide. The cubic root of 21511051 is about 278.1125219500.

Adding to 21511051 its reverse (15011512), we get a palindrome (36522563).

The spelling of 21511051 in words is "twenty-one million, five hundred eleven thousand, fifty-one".