21315765 has 16 divisors (see below), whose sum is σ = 34167168. Its totient is φ = 11347776.

The previous prime is 21315761. The next prime is 21315793. The reversal of 21315765 is 56751312.

It is not a de Polignac number, because 21315765 - 2² = 21315761 is a prime.

It is a Curzon 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 15 ways as a sum of consecutive naturals, for example, 11064 + ... + 12846.

It is an arithmetic number, because the mean of its divisors is an integer number (2135448).

Almost surely, 2^21315765 is an apocalyptic number.

It is an amenable number.

21315765 is a deficient number, since it is larger than the sum of its proper divisors (12851403).

21315765 is a wasteful number, since it uses less digits than its factorization.

21315765 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2588.

The product of its digits is 6300, while the sum is 30.

The square root of 21315765 is about 4616.8999339384. The cubic root of 21315765 is about 277.2683563195.

The spelling of 21315765 in words is "twenty-one million, three hundred fifteen thousand, seven hundred sixty-five".