21315751 has 4 divisors (see below), whose sum is σ = 21339072. Its totient is φ = 21292432.

The previous prime is 21315719. The next prime is 21315761. The reversal of 21315751 is 15751312.

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 21315751 - 2⁵ = 21315719 is a prime.

It is a super-2 number, since 2×21315751² = 908722481388002, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315761) 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, 10231 + ... + 12136.

It is an arithmetic number, because the mean of its divisors is an integer number (5334768).

Almost surely, 2^21315751 is an apocalyptic number.

21315751 is a deficient number, since it is larger than the sum of its proper divisors (23321).

21315751 is an equidigital number, since it uses as much as digits as its factorization.

21315751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23320.

The product of its digits is 1050, while the sum is 25.

The square root of 21315751 is about 4616.8984177692. The cubic root of 21315751 is about 277.2682956170.

The spelling of 21315751 in words is "twenty-one million, three hundred fifteen thousand, seven hundred fifty-one".