21783661 has 4 divisors (see below), whose sum is σ = 21796992. Its totient is φ = 21770332.

The previous prime is 21783659. The next prime is 21783667. The reversal of 21783661 is 16638712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21783661 - 2¹ = 21783659 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21783667) 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, 3805 + ... + 7618.

It is an arithmetic number, because the mean of its divisors is an integer number (5449248).

Almost surely, 2^21783661 is an apocalyptic number.

It is an amenable number.

21783661 is a deficient number, since it is larger than the sum of its proper divisors (13331).

21783661 is a wasteful number, since it uses less digits than its factorization.

21783661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13330.

The product of its digits is 12096, while the sum is 34.

The square root of 21783661 is about 4667.2969693389. The cubic root of 21783661 is about 279.2824356063.

The spelling of 21783661 in words is "twenty-one million, seven hundred eighty-three thousand, six hundred sixty-one".