21233781 has 12 divisors (see below), whose sum is σ = 30727840. Its totient is φ = 14129640.

The previous prime is 21233753. The next prime is 21233813. The reversal of 21233781 is 18733212.

It is not a de Polignac number, because 21233781 - 2⁹ = 21233269 is a prime.

It is a super-2 number, since 2×21233781² = 901746911111922, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21233081) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3810 + ... + 7548.

Almost surely, 2^21233781 is an apocalyptic number.

It is an amenable number.

21233781 is a deficient number, since it is larger than the sum of its proper divisors (9494059).

21233781 is a wasteful number, since it uses less digits than its factorization.

21233781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4376 (or 4373 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21233781 is about 4608.0126952950. The cubic root of 21233781 is about 276.9124261039.

Adding to 21233781 its reverse (18733212), we get a palindrome (39966993).

The spelling of 21233781 in words is "twenty-one million, two hundred thirty-three thousand, seven hundred eighty-one".