21812105 has 24 divisors (see below), whose sum is σ = 32245128. Its totient is φ = 14074368.

The previous prime is 21812083. The next prime is 21812107. The reversal of 21812105 is 50121812.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 8357881 + 13454224 = 2891^2 + 3668^2 .

It is not a de Polignac number, because 21812105 - 2⁸ = 21811849 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21812107) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1547 + ... + 6783.

It is an arithmetic number, because the mean of its divisors is an integer number (1343547).

Almost surely, 2^21812105 is an apocalyptic number.

It is an amenable number.

21812105 is a deficient number, since it is larger than the sum of its proper divisors (10433023).

21812105 is a wasteful number, since it uses less digits than its factorization.

21812105 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5273 (or 5266 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 20.

The square root of 21812105 is about 4670.3431351454. The cubic root of 21812105 is about 279.4039403512.

Adding to 21812105 its reverse (50121812), we get a palindrome (71933917).

The spelling of 21812105 in words is "twenty-one million, eight hundred twelve thousand, one hundred five".