21513761 has 8 divisors (see below), whose sum is σ = 22229544. Its totient is φ = 20805120.

The previous prime is 21513749. The next prime is 21513769. The reversal of 21513761 is 16731512.

It can be written as a sum of positive squares in 4 ways, for example, as 15062161 + 6451600 = 3881^2 + 2540^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21513761 - 2⁶ = 21513697 is a prime.

It is a Duffinian number.

It is a zygodrome in base 3.

It is a self number, because there is not a number n which added to its sum of digits gives 21513761.

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 7 ways as a sum of consecutive naturals, for example, 4721 + ... + 8081.

It is an arithmetic number, because the mean of its divisors is an integer number (2778693).

Almost surely, 2^21513761 is an apocalyptic number.

It is an amenable number.

21513761 is a deficient number, since it is larger than the sum of its proper divisors (715783).

21513761 is a wasteful number, since it uses less digits than its factorization.

21513761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3571.

The product of its digits is 1260, while the sum is 26.

The square root of 21513761 is about 4638.2928971767. The cubic root of 21513761 is about 278.1242004943.

The spelling of 21513761 in words is "twenty-one million, five hundred thirteen thousand, seven hundred sixty-one".