21520751 has 6 divisors (see below), whose sum is σ = 25034400. Its totient is φ = 18446316.

The previous prime is 21520747. The next prime is 21520771. The reversal of 21520751 is 15702512.

It is a happy number.

It is not a de Polignac number, because 21520751 - 2² = 21520747 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520721) 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, 219551 + ... + 219648.

It is an arithmetic number, because the mean of its divisors is an integer number (4172400).

Almost surely, 2^21520751 is an apocalyptic number.

21520751 is a deficient number, since it is larger than the sum of its proper divisors (3513649).

21520751 is an equidigital number, since it uses as much as digits as its factorization.

21520751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439213 (or 439206 counting only the distinct ones).

The product of its (nonzero) digits is 700, while the sum is 23.

The square root of 21520751 is about 4639.0463459638. The cubic root of 21520751 is about 278.1543188551.

The spelling of 21520751 in words is "twenty-one million, five hundred twenty thousand, seven hundred fifty-one".