21781283 has 4 divisors (see below), whose sum is σ = 21803880. Its totient is φ = 21758688.

The previous prime is 21781273. The next prime is 21781289. The reversal of 21781283 is 38218712.

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 21781283 - 2¹⁶ = 21715747 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21781289) 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, 9785 + ... + 11802.

It is an arithmetic number, because the mean of its divisors is an integer number (5450970).

Almost surely, 2^21781283 is an apocalyptic number.

21781283 is a deficient number, since it is larger than the sum of its proper divisors (22597).

21781283 is a wasteful number, since it uses less digits than its factorization.

21781283 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22596.

The product of its digits is 5376, while the sum is 32.

The square root of 21781283 is about 4667.0422110797. The cubic root of 21781283 is about 279.2722726712.

Adding to 21781283 its reverse (38218712), we get a palindrome (59999995).

The spelling of 21781283 in words is "twenty-one million, seven hundred eighty-one thousand, two hundred eighty-three".