21513765 has 32 divisors (see below), whose sum is σ = 42368256. Its totient is φ = 9077760.

The previous prime is 21513749. The next prime is 21513769. The reversal of 21513765 is 56731512.

It is not a de Polignac number, because 21513765 - 2⁴ = 21513749 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21513769) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 6516 + ... + 9245.

It is an arithmetic number, because the mean of its divisors is an integer number (1324008).

Almost surely, 2^21513765 is an apocalyptic number.

It is an amenable number.

21513765 is a deficient number, since it is larger than the sum of its proper divisors (20854491).

21513765 is a wasteful number, since it uses less digits than its factorization.

21513765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15789.

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

The square root of 21513765 is about 4638.2933283698. The cubic root of 21513765 is about 278.1242177313.

The spelling of 21513765 in words is "twenty-one million, five hundred thirteen thousand, seven hundred sixty-five".