21787609 has 4 divisors (see below), whose sum is σ = 21898404. Its totient is φ = 21676816.

The previous prime is 21787607. The next prime is 21787651. The reversal of 21787609 is 90678712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19114384 + 2673225 = 4372^2 + 1635^2 .

It is a cyclic number.

It is not a de Polignac number, because 21787609 - 2¹ = 21787607 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21787603) 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, 55102 + ... + 55495.

It is an arithmetic number, because the mean of its divisors is an integer number (5474601).

Almost surely, 2^21787609 is an apocalyptic number.

It is an amenable number.

21787609 is a deficient number, since it is larger than the sum of its proper divisors (110795).

21787609 is a wasteful number, since it uses less digits than its factorization.

21787609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 110794.

The product of its (nonzero) digits is 42336, while the sum is 40.

The square root of 21787609 is about 4667.7198930527. The cubic root of 21787609 is about 279.2993066678.

The spelling of 21787609 in words is "twenty-one million, seven hundred eighty-seven thousand, six hundred nine".